Reading USGS Topographic Maps
(Adapted from USGS Mapping Advisory Center)  -  http://mac.usgs.gov/mac/

Map Symbols

Elevation

Boundaries

Land Surface Features

Water Features

Buildings & Related Features

Roads, Railroads, and Other

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 Colored lines, areas, and symbols on U.S. Geological Survey (USGS) topographic maps have explicit meanings. Features may be shown as points, lines, or areas, depending on their size; e.g., a single residential house may be depicted by a small black square, while the actual shape of a large building may be mapped. In densely urbanized areas, individual buildings may be omitted and the area shown by tinting, or landmark buildings such as post offices, churches, and city halls may be shown within the tinted area.  Notable tinting on topo maps include green for vegetation, blue for water, purple for updated areas, and grey or red for densely urbanized areas.

Features are often shown by solid, dashed, or dotted lines of various colors: brown topographic contours; blue lakes, streams, irrigation ditches, etc.; red land grids and important roads; and black for other roads and trails, railroads, boundaries, etc.  Point symbols depict buildings, campgrounds, mines, springs, water tanks, and wells.   Place names are shown in various colors corresponding to the type of feature. 
 
Illustration of ground configuration shown by contours

Illustration of ground configuration shown by contours

Ground Configuration shown by contours

Topographic contours (brown lines) are lines of equal elevation that show the shape of the terrain. Index contours (usually every fourth or fifth contour) are wider or darker. Contours that are very close together represent steep slopes, while widely spaced contours or an absence of contours, represent relatively level ground slopes. The contour interval (elevation change between adjacent contour lines) is usually printed near the scale.  A map of a relatively flat area may have a contour interval of 10 feet or less, while a map of a mountainous area may have a contour interval of 100 feet or more. Elevations are printed at frequent intervals on index contour lines to allow interpolation of elevations of adjacent contours.  Bathymetric contours shown in blue or black give the shape and slopes of the bottom of water bodies. 

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