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Topographic maps, also called '''contour maps''', topo maps or topo quads (for quadrangles), are Map s that show Topography , or land contours, by means of Contour Line s. Contour lines are Curve s 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 Vs: 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 Os: 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 Stream s or other bodies of Water , Forest cover, built-up areas or individual buildings (depending on scale), and other features and points of interest.

Topographic maps are prepared using Aerial Photography .


SOURCES OF TOPOGRAPHIC MAPS


United States

The in addition to latitude and longitude and UTM Grids . There are also other series, including some county maps and maps of special interest areas, such as the Grand Canyon , and there are also smaller-scale maps showing much larger areas.

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, as well as DEM datasets that digitally describe topology.


United Kingdom

The Ordnance Survey produces topographic map series covering the United Kingdom at 1:25,000 and 1:50,000. They have a mapping database from which they can print specialist maps at any scale.


France

The Institut Géographique National produces topographic maps of France at 1:25,000 and 1:50,000.


Switzerland

The Federal Office Of Topography produces topographic maps of Switzerland at seven different scales.


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.


SEE ALSO



SOURCES OF TOPOGRAPHIC MAPS



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