Topographic map

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It has been suggested that Cartographic relief depiction be merged into this article or section. (Discuss)
Example of a topographic map with contour lines
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Example of a topographic map with contour lines
Part of the same map in a perspective shaded relief view illustrates how the contour lines of the original follow the terrain
Enlarge
Part of the same map in a perspective shaded relief view illustrates how the contour lines of the original follow the terrain

Topographic maps are a variety of map characterized by large-scale detail and quantitative representation of relief, usually using contour lines in modern mapping, but historically using a variety of methods. Traditional definitions require a topographic map to show both natural and man-made features,[1] [2] but the representation of relief is popularly held to define the genre, such that even small-scale maps showing relief are commonly called "topographic."

Contents

[edit] History

Topographic maps are based on topographical surveys. Performed at large scales, these surveys are called topographical in the old sense of topography, showing a variety of landmark and landscape information.[3] This is in contrast to older cadastral surveys, which primarily show property and governmental boundaries. The first multi-sheet topographic map series of an entire country, the Carte géométrique de la France, was completed in 1789.[4] Topographic surveys were prepared by the military to assist in planning for battle and for defensive emplacements (thus the name and history of the United Kingdom's Ordnance Survey).[5] As such, elevation information was of vital importance.

As they evolved, topographic map series became a basic national resource in modern nations in planning infrastructure and resource exploitation. In the United States, the national map-making function migrated from the Army Corps of Engineers to the United States Geological Survey in 1878, where it has remained since.

[edit] Map Conventions

Topographic maps are also commonly called contour maps or "topo maps." In the United States, where the primary national series is organized by a strict 7.5° grid, they are often called topo quads (or quadrangles).

Topographic maps conventionally show topography, or land contours, by means of contour lines. Contour lines are curves that connect contiguous points of the same altitude (isohypse). In other words, every point on the marked line of 100 m elevation is 100 m above mean sea level.

There are several rules to note when viewing topographic maps:

  • The rule of V's: sharp-pointed vees usually are in stream valleys, with the drainage channel passing through the point of the vee, with the vee pointing upstream. This is a consequence of erosion.
  • The rule of O's: closed loops are normally uphill on the inside and downhill on the outside, and the innermost loop is the highest area. If a loop instead represents a depression, some maps note this by short lines radiating from the inside of the loop, called "hachures".
  • Spacing of contours: close contours indicate a steep slope; distant contours a shallow slope. Two or more contour lines merging indicates a cliff.

Of course, to determine differences in elevation between two points, the contour interval, or distance in altitude between two adjacent contour lines, must be known, and this is given at the bottom of the map. In most cases, contour intervals are consistent throughout a map. Sometimes dashed contour lines are present; these represent half the noted contour interval.

These maps usually show not only the contours, but also any significant streams or other bodies of water, forest cover, built-up areas or individual buildings (depending on scale), and other features and points of interest.

Today, topographic maps are prepared using photogrammetric interpretation of aerial photography. Older topographic maps were prepared using traditional surveying instruments.

[edit] Publishers of national topographic map series

Most countries have some sort of national mapping program. Those listed below are only a small selection. Several commercial vendors supply international topographic map sets. Look for their general indexes at:

[edit] Canada

The Centre for Topographic Information produces topographic maps of Canada at scales of 1:50,000 and 1:250,000. They are known as the National Topographic System (NTS).[6]

[edit] Denmark

The National Survey and Cadastre of Denmark is responsible for producing topographic and nautical geodata of Denmark, Greenland and the Faroe Islands.[7]

[edit] France

The Institut Géographique National (or IGN) produces topographic maps of France at 1:25,000 and 1:50,000.[8]

[edit] India

The Survey of India is responsible for all topographic control, surveys and mapping of India.[9]

[edit] Switzerland

Swisstopo (the Federal Office of Topography) produces topographic maps of Switzerland at seven different scales.

[edit] United Kingdom

The Ordnance Survey (or OS) produces topographic map series covering the United Kingdom at 1:25,000 and 1:50,000. The 1:25K and 1:50K metric scales are easily coordinated with standard romer scales on currently available compasses and plotting tools. They have a mapping database from which they can print specialist maps at any scale.[10]

[edit] United States

The United States Geological Survey (or USGS) produces several national series of topographic maps which vary in scale and extent, with some wide gaps in coverage, notably the complete absence of 1:50,000 scale topographic maps or their equivalent. The largest (both in terms of scale and quantity) and best-known topographic series is the 7.5-minute, 1:24,000 scale, quadrangle, a non-metric scale virtually unique to the United States. Each of these maps covers an area bounded by two lines of latitude and two lines of longitude spaced 7.5 minutes apart. Nearly 57,000 individual maps in this series cover the 48 contiguous states, Hawaii, U. S. territories, and areas of Alaska near Anchorage, Fairbanks, and Prudhoe Bay. The area covered by each map varies with the latitude of its represented location due to convergence of the meridians. At lower latitudes, near 30° north, a 7.5-minute quadrangle contains an area of about 64 square miles. At 49° north latitude, 49 square miles are contained within a quadrangle of that size. As a unique non-metric map scale, the 1:24,000 scale naturally requires a separate and specialized romer scale for plotting map positions.[11]

An older series of maps, the 15-minute series, was used to map the contiguous states at a scale of 1:62,500, but was discontinued some time ago for maps covering the continental U.S. Each map was bounded by two parallels and two meridians spaced 15 minutes apart - the same area covered by four maps in the 7.5-minute series. The 15-minute series, at a scale of 1:63,360 (one inch representing one mile), remains the primary topographic quadrangle for the state of Alaska (and only for that particular state). Nearly 3,000 maps cover 97% of the state.[11] The U.S. remains virtually the only developed country in the world without a standardized civilian topographic map series in the standard 1:25,000 or 1:50,000 metric scales, making coordination difficult in border regions (the U.S. military does issue 1:50,000 scale maps of the continental U.S., though only for use by members of its defense forces).

The next-smallest topographic series, in terms of scale, is the 1:100,000 series. These maps are bounded by two lines of longitude and two lines of latitude. However, in this series, the lines of latitude are spaced 30 minutes apart and the lines of longitude are spaced 60 minutes, which is the source of another name for these maps; the 30 x 60-minute quadrangle series. Each of these quadrangles covers the area contained within 32 maps in the 7.5-minute series. The 1:100,000 scale series is unusual in that it employs the Metric system primarily. One centimeter on the map represents one kilometer of distance on the ground. Contour intervals, spot elevations, and horizontal distances are also specified in meters.

The final regular quadrangle series produced by the USGS is the 1:250,000 scale topographic series. Each of these quadrangles in the conterminous United States measures 1 degree of latitude by 2 degrees of longitude. This series was produced by the U.S. Army Map Service in the 1950s, prior to the maps in the larger-scale series, and consists of 489 sheets, each covering an area ranging from 8,218 square miles at 30° north to 6,222 square miles at 49° north.[11] Hawaii is mapped at this scale in quadrangles measuring 1° by 1°.

USGS topographic quadrangle maps are marked with grid lines and tics around the map collar which make it possible to identify locations on the map by several methods, including the graticule measurements of longitude and latitude, the township and section method within the Public Land Survey System, and cartesian coordinates in both the State Plane Coordinate System and the Universal Transverse Mercator coordinate system.

Other specialty maps have been produced by the USGS at a variety of scales. These include county maps, maps of special interest areas, such as the national parks, and areas of scientific interest.

A number of Internet sites have made these maps available on the web for affordable commercial and professional use. Because works of the U.S. Government are in the public domain, it is also possible to find many of these maps for free at various locations on the Internet. Georeferenced map images are available from the USGS as digital raster graphics (DRGs), in addition to digital data sets based on USGS maps (notably Digital Line Graphs (DLGs) and digital elevation models (DEMs)).

[edit] The Moon

The United States Geological Survey has produced a map of the Moon.[12]

[edit] Commercial publishers of topographic maps

A number of commercial publishers have created topographic maps of recreation areas, with enhanced and updated trails and facilities data on the map, and with supplementary text and graphic information about them. These publishers include:

  • The National Geographic Society's Trails Illustrated Series. Originally founded as a separate company and purchased by National Geographic in the late 1990s.
  • Tom Harrison, a California map publisher, mostly makes maps of California.
  • The Alpine Mapping Guild has published a number of titles for mountaineers, especially of mountain areas in Central Asia and the Andes.

[edit] Global 1-kilometer map

This map is derived from GTOPO30 data that describes the elevation of Earth's terrain at intervals of 30 arcseconds (approximately 1 km). It uses color and shading instead of contour lines to indicate elevation.

N60-90, W150-180 N60-90, W120-150 N60-90, W90-120 N60-90, W60-90 N60-90, W30-60 N60-90, W0-30 N60-90, E0-30 N60-90, E30-60 N60-90, E60-90 N60-90, E90-120 N60-90, E120-150 N60-90, E150-180
N30-60, W150-180 N30-60, W120-150 N30-60, W90-120 N30-60, W60-90 N30-60, W30-60 N30-60, W0-30 N30-60, E0-30 N30-60, E30-60 N30-60, E60-90 N30-60, E90-120 N30-60, E120-150 N30-60, E150-180
N0-30, W150-180 N0-30, W120-150 N0-30, W90-120 N0-30, W60-90 N0-30, W30-60 N0-60, W0-30 N0-60, E0-30 N0-60, E30-60 N0-60, E60-90 N0-60, E90-120 N0-60, E120-150 N0-60, E150-180
S0-30, W150-180 S0-30, W120-150 S0-30, W90-120 S0-30, W60-90 S0-30, W30-60 S0-30, W0-30 S0-30, E0-30 S0-30, E30-60 S0-30, E60-90 S0-30, E90-120 S0-30, E120-150 S0-30, E150-180
S30-60, W150 S30-60, W120 S30-60, W90-120 S30-60, W60-90 S30-60, W30-60 S30-60, W0-30 S30-60, E0-30 S30-60, E30-60 S30-60, E60-90 S30-60, E90-120 S30-60, E120-150 S30-60, E150-180
S60-90, W150-180 S60-90, W120-150 S60-90, W90-120 S60-90, W60-90 S60-90, W30-60 S60-90, W0-30 S60-90, E0-30 S60-90, E30-60 S60-90, E60-90 S60-90, E90-120 S60-90, E120-150 S60-90, E150-180
Each tile is available at a resolution of 1800 × 1800 pixels (approximate file size 1MB, 60 pixels = 1 degree, 1 pixel = 1 minute)

[edit] See also

[edit] Notes and references

  1. ^ "A topographic map is a detailed and accurate graphic representation of cultural and natural features on the ground." Centre for Topopgraphic Information - Topographic Maps: Frequently Asked Questions
  2. ^ "Traditionally, the main division of maps is into topographic and thematic maps. Topographic maps supply a general image of the earth's surface: roads, rivers, buildings, often the nature of the vegetation, the relief and the names of the various mapped objects." M.-J. Kraak and F. Ormeling, Cartography: Visualization of Spatial Data, Longman, 1996, ISBN 0-582-25953-3, p. 44.
  3. ^ The range of information is indicated by the title of a map produced in 1766: A Topographical Map of Hartfordshire from an Actual Survey in which is Express'd all the Roads, Lanes, Churches, Noblemen and Gentlemen's Seats, and every Thing remarkable in the County, by Andrew Dury and John Andrews, reprinted by Hertfordshire Publications in 1980. This showed the relief by using hachures.
  4. ^ Library of Congress: Geography and Maps, General Collections
  5. ^ Peter Barber, The Map Book, Weidenfeld & Nicolson, 2005, ISBN 0-297-84372-9, pp. 232, 250.
  6. ^ Centre for Topographic Information website.
  7. ^ Kort & Matrikelstyrelsens website (in Danish).
  8. ^ Institut Géographique National website (in French, English and German).
  9. ^ Department of Scientific and Technology: Survey of India
  10. ^ Ordnance Survey website. The MasterMap Topography Layer contains information about buildings, roads, woodland, administrative boundaries, etc, with just a few spot heights along the roads. For contours or a digital terrain model, a separate product called Land-Form Profile is required.
  11. ^ a b c USGS Topographic Maps and USGS Maps Booklet.
  12. ^ Color-Coded Topography and Shaded Relief Map of the Lunar Near Side and Far Side Hemispheres.

[edit] External links

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