A map is a representation of the Earth, or part of it. 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. It gives
o measure the height of mountains,
o depths of the ocean bottom, and
o steepness of slopes.
The map includes symbols that represent such features as streets, buildings, streams, and vegetation.
Reading Topographic Maps
o Interpreting the colored lines, areas, and other symbols is the first step in using topographic maps.
o 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.
o 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.
o 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).
o 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). At one time, purple was used as a revision color to show all feature changes. Currently, purple is not used in our revision program, but purple features are still present on many existing maps.
o Many features are identified by labels, such as "Substation" or "Golf Course."
o Topographic contours are shown in brown by lines of...