Topographic Maps!!!

by
Lea Meyer

April 2, 2002

What is a Map?

A map is a representation of the Earth, or part of it. Traditionally, maps have been printed on paper. When a printed map is scanned, the computer file that is created may be called a digital raster graphic.

What Distinguishes a Topographic Map?

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. Topographic maps use a wide variety of symbols (this is an external link to the UC Berkeley Library) to represent human and physical features. (More information on map symbols is given at the USGS site, http://mac.usgs.gov/mac/isb/pubs/booklets/symbols/.) Among the most striking is the map display of the topography or terrain of the area. Contour lines are used to represent elevation by connecting points of equal elevation. These imaginary lines do a nice job of representing the terrain. When contour lines lie close together, they represent a steep slope; lines far apart represent a gradual slope. Each quadrangle uses a contour interval (the distance in elevation between contour lines) appropriate for that area. While flat areas may be mapped with a five-foot contour interval, rugged terrain may have a 100-foot or more contour interval.

Do Topographic Map's Shows More Than Contours?

The map includes symbols that represent such features as streets, buildings, streams, and woods. These symbols are constantly refined to better relate to the features they represent, improve the appearance or readability of the map, or to 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 type styles. On one type of large-scale topographic map, called provisional, some symbols and lettering are hand drawn.

Need some hints in reading a Topographic Map?

  1. Thin brown lines represent contours or points of similar elevation. The closer together they are, the steeper the terrain.
  2. Contour lines form "v" shapes in valleys or along streambeds. The point of the "v" points uphill, therefore the river/stream flows in the opposite direction.
  3. Closed contours shown as ellipses or circles represent hills; closed contours shown with hachures that point downslope, represent a closed depression with no outlet.
  4. Blue represents water.
  5. Green represents orchards and forested areas.
  6. Purple markings are those that have been photorevised or added to the map since the original map was published.
  7. Red or pink areas represent urban areas, although the maps will often indicate special buildings of significance within the urbanized area.
  8. Roads and highways are represented in black and red.
  9. The scale on 1:24,000 topographic maps means that one inch equals 2000 feet

 

Links

Want to do a live chat about Topographic Maps?

http://members.tripod.com/~topomaps/

Looking for a Topographic Map?

http://www.topozone.com/

References:
  • www.geography.about.com/cs/topographicmaps/index_2.htm

  • www.csus.edu/indiv/s/slaymaker/

  • Johnston, P., Aber, S.W., Sleezer, R., and Morales, M. Introduction to Earth Science Lab. Emporia State University, 2001.

    lmitchl@hotmail.com . Return to the ES 111 Student Webpages.