Types of contour lines: How to Read a Topographic Map? Common Topographic Map Symbols.

A topographic map is printed on a flat piece of paper yet it provides a picture of the terrain and manmade features through the use of contour lines, colors, and symbols. Contour lines represent the shape and elevation of the land, such as ridges, valleys, and hills. Colors and symbols are used to represent other features on the land, such as water, vegetation, roads, boundaries, urban areas, and structures.

This chapter starts with tips on how to read the margins of a topographic map. Then it describes how to interpret contour lines. Finally, it covers how to estimate slope, aspect, acreage, distances, and percent contained using a topographic map

What is a topographic map?

Common Topographic Map Symbols:

A topographic map is a detailed and accurate illustration of man-made and natural features on the ground such as roads, railways, power transmission lines, contours, elevations, rivers, lakes and geographical names.

The topographic map is a two-dimensional representation of the Earth’s three-dimensional landscape. The most frequently used topographic map is at a scale of 1:50 000.

Reading a topographic map worksheet

Different maps serve different purposes. If you’re trying to drive from Point A to Point B, a regular road map is a way to go. But if you’ve strayed from the road, perhaps on a backpacking trek, you need to see the terrain and the contours of the land. And that means you need to be able to read a topographic map.

Common Topographic Map Symbols: What’s the difference between a topographic map and a regular map?

In a nutshell, topographic maps allow you to see a three-dimensional landscape on a two-dimensional surface. These maps show the land’s contours, elevations, mountains, valleys, bodies of water, vegetation and more. This contour and elevation inf­ormation distinguishes them from other maps.

Types of contour lines

The ability to fuse these major factors is the most critical skill one can learn when using a topographic map. The primary purpose of a topographic map is to accurately represent the shape of the Earth’s surface, but the utility doesn’t stop there. Topographic maps also represent streets and trails, vegetation, streams, and every type of feature that may positively or negatively impact your ability to navigate through the terrain.

Contour lines on a map

Common Topographic Map Symbols: Contour lines are imaginary

They are map artifacts used to represent paths or segments of Earth at an equal elevation. These paths and segments are presented as elevations (vertical distance above or below sea level) and reliefs (the shape of terrain features on the Earth’s surface).

Not all contour lines are created equal. Heavier contour lines are known as indexed contour lines and are normally numbered showing elevation. Typically every fifth contour line is an index.

Lighter contour lines, that fall between indexed lines, are known as intermediate contour lines. These lines do not have their elevation given and are found in sets of four between indexed contour lines.

Finally, when the terrain is expansively flat, cartographers will often include supplementary contour lines, which are dashed lines indicating an elevation that is half of the elevation between the contour lines surrounding it. They are typically found where there is little change in elevation.

How to read contour lines

Contour lines indicate the steepness of the terrain. Contour lines connect points that share the same elevation: Where they’re close together (they never intersect), the elevation is changing rapidly in short distance and the terrain is steep. Where contour lines are wide apart, the elevation is changing slowly, indicating a gentle slope.

Contour lines also indicate the shape of the terrain. Roughly concentric circles are probably showing you a peek, and areas between peaks are passes. Studying a topo map of a familiar area is a great way to learn how to match terrain features with the contour lines on a map.

Interpreting Contour Lines

Contour lines on a map show topography or changes in elevation. They reveal the location of slopes, depressions, ridges, cliffs, the height of mountains and hills, and other topographical features. A contour line is a brown line on a map that connects all points of the same elevation. They tend to parallel each other, each approximately the shape of the one above it and the one below it. Compare the topographic map with the landscape perspective.

Topographic map colors

Common Topographic Map Symbols: It’s important to know what kind of terrain and environment you’re traveling into and what the map of that area is telling you.

The color brown is used to denote most contour lines on a map, which are relief features and elevations. Topographic maps use green to denote vegetation such as woods, while blue is used to denote water features like lakes, swamps, rivers, and drainage.

At higher elevations, mountains may be snow-capped year around, or the terrain may actually be a glacier. In each of these cases, contour lines are also drawn in blue. It is, therefore, possible to quickly discern that a particular route from A to B might be more treacherous than operating at a high altitude—the trek might require crampons, an ice axe, and other materials that might not be readily available once in the backcountry.

Finally, black is used to represent man-made objects, including trails. Red is used for man-made features, like main roads or political boundaries, and purple for new changes or updates on the map that weren’t previously represented. Newer maps no longer use purple, but since so many older maps exist, it’s worth mentioning.

Map scales

The map’s scale tells you how detailed your map is. A 1:24000 scale, for example, means one inch equals 24,000 inches in reality. A larger scale, like 1:65,000, means that a map covers a larger area, but that it will have less detail.

Maps also have a representative scale to help you visualize real-world distances. You can use this scale and a string or the edge of your compass to get a rough estimate about hiking distances on your map. (Common Topographic Map Symbols)

Topographic map shading

The color similarity between features does not mean that the features are equivalent. Due north of Lake Raven is the Prairie Branch, another name for a stream. Other names that equate to a stream include kill, run, fork, and brook. What’s interesting about Prairie Branch is that it has led to the formation of a wooded marsh or swamp.

Navigating across Prairie Branch could be difficult. Since this is Texas, expect to run into water moccasins, copperheads, and perhaps the occasional alligator, among all of the other friendly animals that call Sam Houston National Forest home.

Remembering map colors is a fairly trivial task, but remembering the shadings is far more difficult given the sheer number of variations. For this reason, keeping the USGS Topographic Map Symbols–a mere two sheets of paper–behind your map can be a lifesaver. A quick reference to page four of the booklet confirms that Prairie Branch is indeed a submerged wooded marsh or swamp. (Common Topographic Map Symbols)

Latitude and longitude map

Latitude and Longitude (edges of map): Common Topographic Map Symbols

Latitude and longitude lines are indicated with fine black tick marks along the edges of the map. Topographic maps do not show the latitude/longitude lines – just the tick marks.

The numbers next to the tick marks indicate degrees (°), minutes (‘) and seconds (“).

On 1:24,000 scale maps, latitude, and longitude tick marks are indicated every 2.5 minutes.

• Longitude tick marks are on the top and bottom edges of the map and latitude tick marks are on the right and left edges. Note that the degrees may be left off (as an abbreviation) and you may only see the minute and/or second designations.
• Reference coordinates for latitude and longitude (degrees, minutes, and seconds) are black and located on the four corners of the map.
• The intersection of latitude and longitude lines are noted by cross-marks.

When reading latitude/longitude, pay close attention to the units (degrees, minutes, seconds) because it is easy to misread them. Refer to Chapters 3 and 6 for additional information on latitude and longitude.

What is a contour interval?

Contours maps (such as topographic maps) compress the information of a function over a two-dimensional area into a discrete set of closed lines that connect points of equal value (isolines), striking a fine balance between expressiveness and cognitive simplicity.

They allow humans to perform many common-sense reasoning tasks about the underlying function (e.g. elevation).

The contour interval is the difference in elevation between two adjacent contour lines. On USGS maps, contour intervals are usually 1, 5, 10, 20, 40, and 80 feet. If the contour interval is not printed on the map, it can be calculated.

Common Topographic Map Symbols

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A surge tank in hydro-power plants can provide a fundamental feature for the hydraulic design of hydropower projects.

Mainly, they can mitigate the effects of overpressure or water hammer and allow the turbine gates to close faster, reducing generator Overspeed after load shedding.

However, in normal operation, they also have the potential to be detrimental to the control systems of hydroelectric projects.

In reaction to hydraulic turbines, there are several ways to mitigate the magnitude of overpressure or water hammer situations.

For example, fast-acting pressure relief valves such as ring valves have been used.

In addition to the fast-closing of the gates, the magnitude of the pressure is a function of the length of the waterline. In short, the faster the closure and the longer the duct, the greater the overpressure.

Hydro Turbine generator

Water lines to drive turbines are generally not subject to the need for water hammer protection.

This is because they are typically designed with jet deflectors that are weighted to drop between the water jet and the runner buckets, allowing the nozzle valve to close slowly without creating undue pressure or allowing significant Overspeed of the nozzle. the turbine-generator.

Surge tanks (video) are the most common means of protection against excessive water hammer pressure.

These are vertical columns of water with the surface of the water exposed to the atmosphere. They are generally used in the penstock upstream of the turbine, but as close to the turbine as circumstances allow.

If the top of the tank is closed to the atmosphere to create a compensation chamber, these are called accumulators, but they are rarely used in hydroelectric power designs.

How does a surge tank work?

Surge tanks have the advantage of having no moving parts and therefore provide passive protection that is always ready to go.

In fact, they act in two different passive ways. When a positive pressure wave reaches the tank surface, it is reflected back down the duct as a negative wave.

This cancels out the next positive pressure wave to come. Similarly, the surge tank water surface reflects a smaller negative wave downstream, but enough to cancel part of the peak of the next positive pressure wave.

At the same time, part of the flow velocity that is reduced by the reduced opening between the bypass gates is diverted to the surge tank and does not contribute to the overpressure.

This causes the elevation of the water surface in the surge tank to increase dramatically.

However, this increase is not only due to the deviation, but part is due to the recovery of the velocity and the head loss in the pipe.

Once these hydraulic oscillations have been instituted in the surge tank, they can continue until they are dampened by hydraulic losses inside and outside the tank.

Water turbine generator

Hydroelectric power is a relatively new invention, but the mechanical energy of water has been used for more than two millennia. The invention of the wheel was soon followed by the invention of the waterwheel, a device that uses the downward movement of streams, rivers, and other bodies of water to mechanically power another device.

The oldest known version of the water wheel comes from Mesopotamia in the mid-4th century BC. C., a horizontal contraption similar to a propeller that was used to turn millstones to grind flour.

The basic waterwheel mechanism spread throughout much of the Old World (Eurasia and Africa) and took several different forms, but the core concept remained the same. As the watermill was further refined, its energy efficiency increased.

Understanding hydraulics was essential to the development of modern hydroelectricity because when the electrical generator was developed in the late 19th century, it could be combined with hydraulics to generate hydroelectricity.

The earliest hydraulic turbines had a vertical axis and used hydrostatic pressure to expel water from a nozzle, creating a rotational force. In many ways, it served as a prototype for modern hydraulic turbines.

The Industrial Revolution accelerated the evolution toward hydroelectric power as water mills gradually became water turbines.

Generator in hydro power plant

In the mid-19th century, turbine research led to energy efficiencies of over 75% (compared to early waterwheels, which were only 20% efficient). In 1850 the design of the water turbine was improved and achieved an efficiency of 90%.

Its high-efficiency turbines could match the unique flow conditions of individual water bodies. To this day, it remains the most widely used working turbine.

In 1832 the first electric generator was developed. Although the device, called a Faraday disk, was actually inefficient as a generator, it marked an important step in the development of electrical power. The concept behind electrical generators underwent experimentation, adjustment, and refinement throughout the 19th century, culminating in the invention of the modern DC dynamo.

Towards the end of the 19th century, hydroelectric power emerged as the preferred source of electrical power in the US, as the country had many rivers and hydroelectricity was cheap and reliable.

The rest of the world soon caught up, and by 1900, hundreds of small hydroelectric plants were in an operation spread across Europe, Asia, Australia, and South America.

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Bathymetric Survey equipment: Bathymetry is the study of the underwater depth of the lake and ocean floors. In the bathymetric survey, charts are produced to support the safety of surface or sub-surface navigations which usually show seafloor relief or terrain as contour lines (depth contours), and such a chart provides surface navigational information. The survey sets for best description of the submarine topographical
features that may include sound velocity and slope corrections that are more accurate but eliminate the safety bias.

Bathymetric and hydrographic survey

Bathymetric survey equipment are important for many purposes; such include sedimentation purposes to check for accretion or erosion, pre and post dredging bathymetry, that is to determine the existing status of the water body or to ascertain the dredged volume. It can also be done prior to pipeline and cable (laying) positioning, fishing, and other geophysical exploration exercises.

Updating of bathymetric chart is a daunting task and cannot be overpassed due to its importance in estimating or determining temporal changes in an ocean floor which in effect; provides accurate information for public usage, in terms of planning, engineering design, construction, operation, maintenance, and regulation of navigation, flood control, river engineering, charting, and coastal engineering projects.

Resurvey policy especially that of bathymetry gives bounds for the reliability of identified sea erosion and accretion areas, determination of sediment transport pathways, the magnitude of sediment transport estimates, and the validity of sediment budget estimates.

Bathymetric survey cost

Comparison of digital bathymetric data for the same region but different time periods provides a method for estimating or calculating the net movement of sediment into (accretion) and out of (erosion) a study area. Producing a bathymetric chart; tidal observation and reduction is a must to reduce the sounding depth to chart datum.

Tidal observation is conducted prior to and concurrently with sounding operations period and can be done on the established gauge or temporarily on any selected position where the water level hardly goes below the zero reading of the measuring device (Temporary gauge).

The reduction applicable to sounding depth is done based on the rise and fall differential subtraction for gauge data using an instantaneous timing interval for each sounding point. Further processes have to do with spike removal, HYPACK matrix generation and possibly preparation of schema for ideal data structuring; then the production of a bathymetric chart.

A proper environmental impact assessment needs to be done in order to assess the level of impact caused by man and nature, especially as it concerns coastal waters.

The bathymetric survey equipment is important for the production of the up-to-date bathymetric chart, due to mining exercises opined by local miners and licensed dredging companies.

In the absence of mining exercise, there is a need to investigate and account for sediment deposit or eroded, so that proper planning responses can be implemented. It is, therefore, necessary to update the bathymetric chart covering, which would be compared with the earlier bathymetric survey equipment; for investigating sediments (Accretion and Erosion) and dredged region area.

Marine protected areas

Bathymetry surveys are the first step for every conservation effort on Marine Protected Areas (MPAs). Maps depicting depth and bottom geomorphology are used to generate hillsides, that later become base maps for other themes, such as fish distribution, bottom types, and water quality.

Bathymetry map availability is limited or non-existent at the scales that are necessary for MPA management plans. Survey costs by traditional-sounding methods or new technologies, such as LIDAR, are prohibitive for most MPA budgets.

Remote Sensing bathymetry is yet unreliable, except for crystal clear waters. A low-cost technique, based on commercially available GPS-echosounder units was applied to obtain detailed bathymetry of two MPAs in coastal.

Hydrographic survey

Hydrographic Charts as used by seafarers are based on data accumulated over years of professional surveying operations. Standard hydrographic charts either in paper form or as ENC are available for most areas of the world and are quite inexpensive thanks to two factors: government-subsidized hydrographic surveys and a large number of charts printed for numerous users.

Dedicated charts, as produced for the offshore oil & gas industry, coastal engineering, cable-laying operations, etc. cost a similar amount to produce but are much more expensive to buy due to the limited number of users and additional requirements. For these charts, navigational (safe) depth is insufficient; detailed sea bottom morphology is required.

Hydrographic services

In both cases, the basis for the hydrographic charts, bathymetric survey equipment operations, have been and still are a rather costly affair. In the old days they were costly because the instruments used, lead line, sextant and the like, provided only a sounding every now and then whilst ship-time ticked by.

Nowadays bathymetric information is typically gathered from dedicated survey vessels using single or multi-beam echo sounding systems. The prime cost factor in ship-borne surveys is the time and thus the expense involved in conducting the survey and in data post-processing. Delays due to factors such as weather-related downtime, logistics, red tape and instrument breakdown can cause operational costs to go through the roof.

Bathymetric survey equipment cost

The execution of a cost-effective hydrographic survey necessitates the use of a package of three:

• Well trained personnel,
• Accurate, reliable instrumentation and
• A suitable survey vessel.

Bathymetric Survey Equipment: How can we save on these?

Survey personnel has, historically, not been in the top regions of offshore personnel salary scales. There are signs that this is changing gradually (which is necessary to keep enough people in our business!) and the only way to reduce costs here is to deploy personnel on the job.

Thanks to advanced survey systems and computer equipment, this is a possibility, to a certain degree. The other way would be to work longer hours to keep equipment and ship operational for longer periods, but this is done already: for most offshore survey operations, a 24hrs working day is no exception.

The other possibility to optimize survey operations is to deploy more advanced, more productive survey systems. Positioning-wise, we are “on dry ground” already: The horizontal positioning world has been turned upside down in the past 25 years by the implementation of GPS and DGPS.

DGPS survey

Although freely available DGPS has a stated horizontal accuracy of +/-10 meters (95 percent), many mariners are claiming 3-meter or better accuracy with this system. With selective availability set to zero, the most basic GPS receiver in a non-differential mode may offer 10-15 meter horizontal accuracy.

Some sophisticated survey receivers now advertise sub-meter accuracy and with (long-range) RTK systems, the cm accuracy levels can be reached for both horizontal accuracy and vertical referencing.

Echo sounder for bathymetric survey

Bathymetric Survey Equipment: What else can we ask for?

For bathymetric measurements, great improvements have been made the last two decennia. In the past, survey lines were sailed and only the depth directly under the vessel was measured using a single beam echo sounder.

Then, multi-transducer systems were developed whereby an array of transducers was fitted on a pole, fitted perpendicularly onto the vessel, giving a swath width of the length of the pole. The system is still very useful for very shallow water.

Nowadays, we have multi-beam, providing fan-shaped coverage of the seafloor similar to side-scan sonar, but the output data is in the form of depths rather than images.

Multibeam echo sounder

The multi-beam system measures and records the time for the acoustic signal to travel from the transducer to the seafloor and back. For bathymetric purposes, multi-beam transducers are generally attached to a vessel, rather than being towed like a side scan. Therefore, the coverage area on the seafloor is dependent on the depth of the water, typically two to four times the water depth.

The production rate of multi-beam is many times that of a single beam and for an increasing number of (larger) surveys, it became a price decreasing survey tool. Post-processing of the results of this system has still a considerable price impact due to the vast amount of data that is generated, but new processing packages, such as Triton Images’ multi-beam software, are quickly helping to overcome this.

Survey platform

The third, but a major factor of costs is the survey platform. Indeed, it may be well possible to select suitable personnel and equipment for a reasonable price, but the platform on which these have to be placed to perform the work, a ship, is still the major cost-component of bathymetric survey equipment.

Improved ship design, less ship’s crew, higher survey speed, less fuel consumption and on-board data processing and charting may increase the vessel’s cost-effectiveness, but ships remain expensive.

Bathymetric LIDAR system

For certain applications such as surveys in relatively shallow, clean water, Lidar solutions with combined RTK-DGPS / Inertial systems will provide alternatives.

The high speed and enormous amount of data generated enable covering large areas in short survey time. Lightweight Lidar systems (Hawkeye 2) are being developed and smaller airplanes or helicopters can be deployed from remote airfields all over the world to execute such surveys.

For large projects, whereby a multitude of sensors have to be deployed over prolonged periods of time, Zeppelin-type aircraft may become a cost-saving platform: with payloads of over 35 tonnes, the endurance of several weeks in the air and an airspeed of 150 knots, large areas can be surveyed at reasonably low cost.

Survey vessel

Another possible cost-saving alternative for a survey vessel (or in combination with it) is the AUV. This sensor platform can, in certain cases, be deployed from the shore and execute surveys in a stable (underwater) mode at high speed without on-board personnel.

A study of the broader scope of AUV mission applications for the U.S. Navy was recently completed by a US Navy R&D team. The study, which looks ahead 50 years, provides a roadmap to use in integrating AUV’s into the battlespace of the future.

One of the most significant recommendations in the AUV Master Plan was that many missions could be completed using multiple, inexpensive, small AUV’s rather than fewer large and expensive ones.

Nowadays, several research institutes and AUV manufacturers, such as Hafmynd Gavia are working on the development of the deployment of multiple AUV’s from shore or ship. Various operational procedures and survey modes (lawnmower-pattern, Master AUV – multiple slave configuration, etc.), navigation control, testing facilitation, are under development.

Although survey systems will develop even further, personnel costs can be reduced by deploying less personnel and AUV’s, Zeppelins, Survey Vessels, and possible future creations may form a pool of suitable hydrographic sensor/personnel platforms from which the most cost-effective solution can be chosen, it will remain a difficult task to explain why hydrographic surveys are “so expensive”.

Bathymetric study

The term “bathymetry” originally referred to the ocean’s depth relative to sea level, although it has come to mean “submarine topography,” or the depths and shapes of underwater terrain.

In the same way that topographic maps represent the three-dimensional features (or relief) of overland terrain, bathymetric maps illustrate the land that lies underwater. Variations in sea-floor relief may be depicted by color and contour lines called depth contours or isobaths.

Bathymetry is the foundation of the science of hydrography, which measures the physical features of a water body. Hydrography includes not only bathymetry, but also the shape and features of the shoreline; the characteristics of tides, currents, and waves; and the physical and chemical properties of the water itself.

Bathymetric Survey Equipment

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What is an underwater topography maps?

A map is a representation of the Earth or part of it. The distinctive characteristic of a topographic map is that the shape of the Earth’s surface is shown by contour lines. Contours are imaginary lines that join points of equal elevation on the surface of the land above or below a reference surface, such as mean sea level. Contours make it possible to measure the height of mountains, depths of the ocean bottom, and steepness of slopes.

A topographic map shows more than contours. The map includes symbols that represent such features as streets, buildings, streams, and vegetation.

These symbols are constantly refined to better relate to the features they represent, improve the appearance or readability of the map, or reduce production cost. Consequently, within the same series, maps may have slightly different symbols for the same feature.

Examples of symbols that have changed include built-up areas, roads, intermittent drainage, and some lettering styles. On one type of large-scale topographic map, called provisional, some symbols and lettering are hand-drawn.

Underwater topographic maps

Types of Underwater Topography Maps:

Underwater contours

Bathymetric map

Topographic maps of the seafloor. Detailed depth contours provide the size, shape, and distribution of underwater features. The map serves as a tool for performing scientific, engineering, marine geophysical and environmental studies, that are required in the development of energy and marine resources. (Underwater Topography Maps)

Geological survey

Topo/Bathy Maps: Detailed multipurpose maps of NOS bathymetry and US Geological Survey (USGS) land topography. Maps support the Coastal Zone Management and Energy Impact Programs and the offshore oil and gas program.

They may also be used by land-use planners, conservationists, oceanographers, marine geologists, and those interested in the coastal zone and the Outer Continental Shelf’s (OCS) physical environment. All 1:250,000 and 1:1000,000 maps are overprinted with the Minerals Management Service’s OCS Protraction Diagram data. (Underwater Topography Maps)

Bathy fishing maps

Topographic maps of the seafloor produced at a 1:100,000 scale that contains Loran-C rates, bottom sediment types and known bottom obstructions. This product is intended to aid fishermen and those needing seafloor features and potential fishing grounds.

Geophysical mapping

Geophysical Maps: Each consist of three sheets (a base bathymetric map, a magnetic map, and a gravity map), and where practicable a sediment overprint (NOS 1308N-17S). The bathymetric map, when combined with the other three maps, serves as a base for making geological-geophysical studies of the oceans bottom’s crustal geophysical data for the Continental Shelf and slope. The SEAMAP SERIES at a scale of 1:1,000,000, covers geophysical data gathered in the deep-sea area, sometimes including the adjacent Continental Shelf and Slope. (Underwater Topography Maps)

Preliminary Bathymetric Maps

Bathymetric maps that have been compiled, but are not published. NOAA provides blackline copies of compilation manuscripts for bathymetric maps that were left in the production process but are sufficiently developed to include accurate bathymetric data. There are no plans to have these maps published.

Regional Maps

1:1,000,000 scale maps compiled from 1:250,000 scale bathymetric maps.

Reading topographic maps

Underwater contours Maps: Interpreting the colored lines, areas, and other symbols are the first step in using topographic maps. Features are shown as points, lines, or areas, depending on their size and extent. For example, individual houses may be shown as small black squares. For larger buildings, the actual shapes are mapped. In densely built-up areas, most individual buildings are omitted and an area tint is shown. On some maps, post offices, churches, city halls, and other landmark buildings are shown within the tinted area.

The first features usually noticed on a topographic map are the area features, such as

• vegetation (green)
• water (blue), and
• densely built-up areas (gray or red).

Many features are shown by lines that may be straight, curved, solid, dashed, dotted, or in any combination. The colors of the lines usually indicate similar classes of information:

• topographic contours (brown);
• lakes, streams, irrigation ditches, and other hydrographic features (blue);
• land grids and important roads (red); and other
• roads and trails, railroads, boundaries, and other cultural features (black).

Bathymetric contours are shown in blue or black, depending on their location. They show the shape and slope of the ocean bottom surface. The bathymetric contour interval may vary on each map and is explained in the map margin.

Offshore exploration

Exploration in offshore is an important and costly affair for offshore exploration companies. The mighty ocean survey is not only expensive but also be consuming.

Remote sensing has opened up a new tool for offshore exploration. The ocean floor is characterized by the presence of numerous seamounts, atolls, ridges, trenches, etc.

The variation in relief constitutes the morphology of the ocean floor. Charting of the ocean is very important for many reasons: it affects circulation, a potential site for living and non-living resources, submarine navigation, geophysical exploration, etc.

Most areas of the oceans are uncharted because ships could map only a small fraction of the seafloor.

In brief bathymetry is the seafloor-relief.

Undersea topography

Detailed bathymetry data of the seafloor in offshore is sparse as bathymetry data collection is expensive and me-consuming and complete coverage of the whole area by ship is a daunting task to be achieved in the years to come.

Hence, bathymetry prediction using high-resolution satellite gravity may be a viable op on in the unexplored regions. The most commonly used model to relate gravity with bathymetry is a convolution model. Bathymetry, when convolved with a response function, yields geoid or gravity.

The surface of the ocean is a good approximation to the marine geoid. A major contribution to the marine geoid is made by topographic anomalies in the very shallow rock water interface at the base of the ocean because this surface represents the large density contrast. The largest contrasts occur at the earth’s surface and at the ocean bottom (or at the base of the sediments in the ocean) and are affected by seafloor undulations. Consequently, there is a strong correlation between the shape of the geoid and ocean bottom topography.

What is bathymetric data?

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What is a topographic map? Topographic map definition

Topographic maps produced by Natural Resources, offer detailed information on a particular area and are used for several types of activities such as emergency preparedness, urban planning, resource development, and surveying to camping, canoeing, adventure racing, hunting, and fishing.

This guide will help the user understand the basics of topographic maps. The guide provides an overview of mapping concepts, along with tips on how to use a topographic map, explanations of technical terminology and examples of symbols used to represent topographic features on topographic maps.

Why? Topographic maps represent the Earth’s features accurately and to scale on a twodimensional surface. Topographic maps are an excellent planning tool and guide and, at the same time, help make outdoor adventures enjoyable and safe.

Topographic map definition

What is a topographic map? topographic map definition

A topographic map is a detailed and accurate illustration of man-made and natural features on the ground such as roads, railways, power transmission lines, contours, elevations, rivers, lakes and geographical names.

The topographic map is a two-dimensional representation of the Earth’s three-dimensional landscape. The most frequently used Canadian topographic map is at a scale of 1:50 000.

What is a topographic map?

Topographic map definition: What information is on a topographic map?

Topographic maps identify numerous ground features, which can be grouped into the following categories:

• Relief: mountains, valleys, slopes, depressions as defined by contours
• Hydrography: lakes, rivers, streams, swamps, rapids, falls
• Vegetation: wooded areas
• Transportation: roads, trails, railways, bridges, airports/airfield, seaplane anchorages
• Culture: buildings, urban development, power transmission line, pipelines, towers
• Boundaries: international, provincial/territorial, administrative, recreational, geographical
• Toponymy: place names, water feature names, landform names, boundary names

Refer to the map legend for a complete listing of all features and their corresponding symbols. Information along the map borders provides valuable details to help you understand and use a topographic map. For example, here you will find the map scale and other important information about the map such as the year, the edition and information pertaining to the map data.

Topographic map example

Topographic map definition: Is a topographic map similar to a road map?

Both types of maps show roads, water features, cities, and parks, but that’s where the similarity ends.

• Topographic maps show contours, elevation, forest cover, marsh, pipelines, power transmission lines, buildings and various types of boundary lines such as international, provincial and administrative, and many others.
• Topographic maps show a universal transverse Mercator (UTM) grid, allowing the user to determine precise positions. In basic terms, topographic maps allow the user to see a threedimensional landscape on a two-dimensional surface.

Topographic map definition: What do the colors mean?

A variety of colors can be found on a map, each relating to different types of features.

• Black shows cultural features such as buildings, railways, and power transmission lines. It is also used to show geographical names (toponymy), certain symbols, geographic coordinates, and precise elevations.
• Blue represents water features, such as lakes, rivers, falls, rapids, swamps, and marshes. The names of water bodies and watercourses are also shown in blue, as are magnetic declination and UTM grid information.
• Green indicates vegetation such as wooded areas, orchards, and vineyards.
• Some areas are mapped in black and white (monochrome).

Topographic contour lines

Topographic map definition: What are contour lines?

Contour lines connect a series of points of equal elevation and are used to illustrate relief on a map. They show the height of ground above mean sea level (MSL) either in meters or feet and can be drawn at any desired interval. For example, numerous contour lines that are close to one another indicate hilly or mountainous terrain; when further apart they indicate a gentler slope; and when far apart they indicate flat terrain.

Topographic map scale

What is scale? Topographic map definition.

Maps are made to scale. In each case, the scale represents the ratio of a distance on the map to the actual distance on the ground. A standard topographic map is produced at 1:50000, where 2 cm on the map represents 1 km on the ground.

Medium-scale maps (e.g. 1:50 000) cover smaller areas in greater detail, whereas small-scale maps (e.g. 1:250 000) cover large areas in less detail.
A 1:250 000 scale national topographic system (NTS) map covers the same area as sixteen 1:50 000 scale NTS maps.

Measure distance on map

Topographic map definition: How do I measure distance on a map?

Use the scale bar found at the bottom of every NRCan topographic map to determine distances between points or along lines on the map sheet. Use the secondary division on the left of the scale bar for measuring fractions of a kilometer.

Topographic map definition: What is a grid?

A grid is a regular pattern of parallel lines intersecting at right angles and forming squares; it is used to identify precise positions. To help you locate your position accurately on the surface of the Earth (or map sheet), topographic maps have two kinds of referencing systems:

• universal transverse Mercator (UTM) projection (easting/northing)
• geographic: degrees and minutes (longitude/latitude)

The projection used for topographic maps is UTM.

The UTM grid is a square grid system of lines depicted on maps and based on the transverse Mercator projection. It can be used to accurately locate the position of features on the map by distance or direction. To express your location in grid coordinates or geographic coordinates, read the following section.

what features are shown on a topographic map?

Topographic map latitude longitude: How can I find or express a location on a map?

You can find or express a location on a map by using geographic coordinates (longitude, latitude) or by using UTM grid coordinates (easting, northing).

Geographic coordinates are expressed in degrees, minutes and seconds and can be determined on the map by using the longitude and latitude graticules placed along the edges of the map.

Latitude graticules are placed along the east and west edges of the map and longitude graticules are placed along the north and south edges of the map. The longitude and latitude of your location can be determined by projecting your location to the map edges and then by reading the corresponding latitude and longitude values.

UTM grid coordinates are expressed in meters and can be determined on the map by using the UTM grid lines. These grid lines are equally spaced horizontal and vertical lines superimposed over the entire map.

The coordinate value for each grid line can be found along the edge of the map. Northing values can be read along the east or west edges of the map and easting values can be read along the north or south edges of the map. The easting and northing of your location can be determined by projecting your location to the nearest horizontal and vertical grid lines and then reading the corresponding easting and northing values.

GPS latitude and longitude

How can I determine where I am on a map using a GPS receiver?

If you have a GPS receiver, your location can be determined very quickly. This satellite receiving system displays a position in terms of latitude, longitude, and height, providing you with precise coordinates for map reference. (Some receivers also provide direct conversion of position to a selected map grid such as UTM.)

With this GPS coordinate, you can then use the geographic or UTM grid reference system on the map to determine where you are

How can I determine where I am on a map without using a GPS?

If you do not have a GPS receiver, identify as many features around you as you can, man-made or natural, and locate those same features on your map. Then orient the map, in relation to yourself, so that its orientation corresponds to the ground features that you have identified. If this is difficult to do, use a compass to help you orient the map to north and try again to identify surrounding features.

By estimation, or by using a compass, take bearings to the known features and then from the known features, plot the bearing lines. The intersection of these lines should indicate your location.

How to navigate with a compass and a topographic map?

Navigating by compass requires determining bearings with respect to true or grid north from a map sheet and converting them to magnetic bearings for use with a compass.

One way of doing this is described in the following steps:

1. Place the compass on the map with the direction-of-travel arrow pointing along the desired line of travel.
2. Rotate the compass dial so that the parallel lines within the capsule line up with the grid lines on the map. Convert the grid bearing to a magnetic bearing by using the information given (as in the accompanying diagram) on the map sheet. If the declination is west, add it to the grid bearing; if declination is east, subtract it from the grid bearing
3. Adjust the dial to read the value of the magnetic bearing opposite the direction-of-travel arrow. Make certain to account for the difference between grid north and true north.
4. Now pick up and rotate the whole compass until the red end of the needle points to the north marker on the dial. The direction-of-travel arrow on the compass card will point to your destination. Choose a landmark in that direction and walk toward it.

Topographic map definition

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Topographic survey: Surveying has to do with the determination of the relative spatial location of points on or near the surface of the earth.

• It is the art of measuring horizontal and vertical distances between objects, measuring angles between lines, determining the direction of lines, and of establishing points by predetermined angular and linear measurements.
• Along with the actual survey, measurements are the mathematical calculations.
• Distances, angles, directions, locations, elevations, areas, and volumes are thus determined from the data of the survey.
• Survey data is portrayed graphically by the construction of maps, profiles, cross-sections, and diagrams

Fundamentals of land surveying

The importance of the Surveying

Land surveying is basically an art and science of mapping and measuring land. The entire scope of the profession is wide; it actually boils down to calculate where the land boundaries are situated. This is very important as, without this service, there would not have been railroads, skyscrapers could not have been erected and neither any individual could have put fences around their yards for not intruding others land.

Types of a survey in civil

Types of surveying

• Geodetic Surveying:
  • The type of surveying that takes into account the true shape of the earth. These surveys are of high precision and extend over large areas.
• Plane Surveying:
  • The type of surveying in which the mean surface of the earth is considered as a plane, or in which its spheroidal shape is neglected, with regard to horizontal distances and directions.

Different survey methods

Different methods of Surveying:

• Control Survey: Made to establish the horizontal and vertical positions of arbitrary points.
• Boundary Survey: Made to determine the length and direction of landlines and to establish the position of these lines on the ground.
• Topographic Survey: Made to gather data to produce a topographic map showing the configuration of the terrain and the location of natural and man-made objects.
• Hydrographic Survey: The survey of bodies of water made for the purpose of navigation, water supply, or sub-aqueous construction.
• Mining Survey: Made to control, locate and map underground and surface works related to mining operations.
• Construction Survey: Made to lay out, locate and monitor public and private engineering works.
• Route Survey: Refers to those control, topographic, and construction surveys necessary for the location and construction of highways, railroads, canals, transmission lines, and pipelines.
• Photogrammetric Survey: Made to utilize the principles of aerial photogrammetry, in which measurements made on photographs are used to determine the positions of photographed objects.
• Astronomical survey: generally involve imaging or “mapping” of regions of the sky using telescopes. (Topographic survey cost)

Chain surveying

Topographic survey cost: Distance Measuring (Chaining surveying)

English mathematician Edmund Gunter (1581-1626) gave to the world not only the words cosine and cotangent, and the discovery of magnetic variation, but the measuring device called Gunter’s chain shown below. Edmund also gave us the acre which is 10 square chains. The Gunter’s chain is 1/80th of a mile or 66 feet long. It is composed of 100 links, with a link being 0.66 feet or 7.92 inches long. Each link is a steel rod bent into a tight loop on each end and connected to the next link with a small steel ring.

Starting in the early 1900’s surveyors started using steel tapes to measure distances. These devices are still called “chains” to this day.

Chain surveying procedure

Procedure of Chaining

• It must be remembered in surveying, that under most circumstances, all distances are presumed to be horizontal distances and not surface distances.
• This dictates that every field measurement is taken be either measured horizontally or, if not, reduced to a horizontal distance mathematically.
• In many instances, it is easiest to simply measure the horizontal distance by keeping both ends of the chain at the same elevation. This is not difficult if there are less than five feet or so of elevation change between points. A hand level or “pea gun” is very helpful for maintaining the horizontal position of the chain when “level chaining.” A pointed weight on the end of a string called a “plumb bob” is used to carry the location of the point on the ground up to the elevated chain by simply suspending the plumb bob from the chain such that the point of the plumb bob hangs directly above the point on the ground.
• When the difference in elevation along the measurement becomes too great for level chaining, other methods are called for. One option, “break chaining”, involves simply breaking the measurement into two or more measurements that can be chained level. (Topographic survey cost)

Electronic distance meter

Distance Measuring (Electronic Distance Meters)

In the early 1950s, the first Electronic Distance Measuring (EDM) equipment was developed. These primarily consisted of electro-optical (light waves) and electromagnetic (microwave) instruments. They were bulky, heavy and expensive. The typical EDM today uses the electro-optical principle. They are small, reasonably lightweight, highly accurate, but still expensive.

Purpose of chain surveying

Principle of Chaining

• To measure any distance, you simply compare it to a known or calibrated distance; for example by using a scale or tape to measure the length of an object. In EDM’s the same comparison principle is used. The calibrated distance, in this case, is the wavelength of the modulation on a carrier wave.
• Modern EDM’s use the precision of a Quartz Crystal Oscillator and the measurement of phase-shift to determine the distance.
• The EDM is set up at one end of the distance to be measured and a reflector at the other end.
• The EDM generates an infrared continuous-wave carrier beam, which is modulated by an electronic shutter (Quartz crystal oscillator).
• This beam is then transmitted through the aiming optics to the reflector.
• The reflector returns the beam to the receiving optics, where the incoming light is converted to an electrical signal, allowing a phase comparison between transmitted and received signals.
• The amount by which the transmitted and received wavelengths are out of phase can be measured electronically and registered on a meter to within a millimeter or two.

Measuring angles

Angle Measuring: Topographic survey cost

Measuring distances alone in surveying does not establish the location of an object. We need to locate the object in 3 dimensions. To accomplish that we need:

• Horizontal length (distance)
• The difference in height (elevation)
• Angular direction.

An angle is defined as the difference in direction between two convergent lines. A horizontal angle is formed by the directions to two objects in a horizontal plane. A vertical angle is formed by two intersecting lines in a vertical plane, one of these lines horizontal. A zenith angle is the complementary angle to the vertical angle and is formed by two intersecting lines in a vertical plane, one of these lines directed toward the zenith.

Different types of angles

Types of Measured Angles

• Interior angles are measured clockwise or counter-clockwise between two adjacent lines on the inside of a closed polygon figure.
• Exterior angles are measured clockwise or counter-clockwise between two adjacent lines on the outside of a closed polygon figure.
• Deflection angles, right or left, are measured from an extension of the preceding course and the ahead line. It must be noted when the deflection is right (R) or left (L).

Theodolite

A Theodolite is a precision surveying instrument; consisting of an alidade with a telescope and an accurately graduated circle, and equipped with the necessary levels and optical-reading circles. The glass horizontal and vertical circles, optical-reading system, and all mechanical parts are enclosed in an alidade section along with 3 leveling screws contained in a detachable base or tribrach.

Transits

A Transit is a surveying instrument having a horizontal circle divided into degrees, minutes, and seconds. It has a vertical circle or arc. Transits are used to measure horizontal and vertical angles. The graduated circles (plates) are on the outside of the instrument and angles have to be read by using a vernier.

Closed traverse procedure

Procedure for running a traverse: Topographic survey cost

To begin any traverse, a known point must be occupied. (To occupy a point means to set up and level the transit or theodolite, directly over a monument on the ground representing that point.) Next, a direction must be established. This can be done by sighting with the instrument a second known point, or any definite object, which is in a known direction from the occupied point.

The object that the instrument is pointed to in order to establish a direction is known as a backsight. Possible examples would be another monument on the ground, a radio tower or water tank on a distant hill, or anything with a known direction from the occupied point. A celestial body such as Polaris or the sun could also be used to establish an initial direction.

Once the instrument is occupying a known point, for example, point number 2, and the telescope has been pointed toward the backlight, perhaps toward point number 1, then an angle and a distance is measured to the first unknown point. An unknown point being measured is called foresight. With this data, the position of this point (let’s call it point number 100) can be determined.

The next step is to move the instrument ahead to the former foresight and duplicate the entire process.

GPS global positioning system

How satellite distance is measured

The Global Positioning System (GPS) is a navigational or positioning system developed by the United States Department of Defense. It was designed as a fast positioning system for 24 hours a day, three-dimensional coverage worldwide.

It is based on a constellation of 21 active and 3 spare satellites orbiting 10,900 miles above the earth. The GPS (NAVSTAR) satellites have an orbital period of 12 hours and are not in geosynchronous orbit (they are not stationary over a point on the earth). They maintain a very precise orbit and their position is known at any given moment in time.

This constellation could allow GPS user access to up to a maximum of 8 satellites anywhere in the world.

GPS provides Point Position (Latitude/Longitude) and Relative Position (Vector). GPS can differentiate between every square meter on the earth’s surface thus allowing a new international standard for defining locations and directions.

GPS satellite system

The Principles of GPS

For centuries man has used the stars to determine his position. The extreme distance from the stars made them look the same from different locations and even with the most sophisticated instruments could not produce a position closer than a mile or two. The GPS system is a constellation of Manmade Stars at an orbit high enough to allow a field of view of several satellites, yet low enough to detect a change in the geometry even if you moved a few feet.

A typical conventional survey establishes positions of unknown points by occupying a known point and measuring the unknown points. GPS is somewhat the opposite.

GPS stands for a global positioning system

How satellite distance is measured

Each GPS satellite continually broadcasts a radio signal. Radio waves travel at the speed of light (186,000 miles per second) and if we measure how long it took for the signal to reach us we could compute the distance by multiplying the time in seconds by 186,000 miles per second.

In order to measure the travel time of the radio signal, the satellite broadcasts a very complicated digital code. The receiver on the ground generates the same code at the exact time and when the signal is received from the satellite, the receiver compares the two and measures the phase shift to determine the time difference.

Differential GPS

To achieve sub-centimeter accuracies in positions, we need a survey-grade receiver and a technique called Differential GPS. By placing a receiver at a known location, a total error factor that accounts for all the possible errors in the system can be computed which can be applied to the position data of the other receivers in the same locale. The satellites are so high-up that any errors measured by one receiver could be considered to be exactly the same for all others in the immediate area.

Boundary and topographic survey cost

Differential leveling

Differential leveling is the process used to determine a difference in elevation between two points. A Level is an instrument with a telescope that can be leveled with a spirit bubble. The optical line of sight forms a horizontal plane, which is at the same elevation as the telescope crosshair.

By reading a graduated rod held vertically on a point of known elevation (Bench Mark) a difference in elevation can be measured and a height of instrument (H.I.) calculated by adding the rod reading to the elevation of the benchmark. Once the height of the instrument is established, rod readings can be taken on subsequent points and their elevations calculated by simply subtracting the readings from the height of the instrument.

Digital terrain model

A digital Terrain Model (DTM) is a numerical representation of the configuration of the terrain consisting of a very dense network of points of known X, Y, Z coordinates. Modern surveying and photogrammetric equipment enable rapid three-dimensional data acquisition. A computer processes the data into a form from which it can interpolate a three-dimensional position anywhere within the model.

Think of a DTM as an electronic lump of clay shaped into a model representing the terrain. If alignment was draped on the model and a vertical cut made along the line, a side view of the cut line would yield the alignment’s original ground profile. If vertical cuts were made at right angles to the alignment at certain prescribed intervals, the side views of the cuts would represent cross-sections. If horizontal cuts were made at certain elevation intervals, the cut lines when viewed from above would represent contours.

A DTM forms the basis for modern highway location and design. It is used extensively to extract profiles and cross-sections, analyze alternate design alignments, compute earthwork, etc.

Topographic cross-section

Cross-sections are lines 90 degrees perpendicular to the alignment (P-Line, L-Line, the centerline of stream, etc.), along which the configuration of the ground is determined by obtaining elevations of points at known distances from the alignment.

Cross-sections are used to determine the shape of the ground surface through the alignment corridor. The shape of the ground surface helps the designer pick his horizontal and vertical profile. Once the alignment is picked, earthwork quantities can be calculated. The earthwork quantities will then be used to help evaluate the alignment choice.

In addition to earthwork calculations, cross-sections are used in the design of storm sewers, culvert extensions and the size and location of new culverts.

Topographic survey cost

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