The Information Contained in Topographic Maps

Contours make it possible for the user of a USGS quad map to determine the height of mountains, depths of the ocean bottom (bathymetric maps), and steepness of slopes. A topographic map shows more than contours. The elevations of tops of mountains are often shown, elevations of ponds or borrow sites, and of key cultural features of interest. A USGS map includes symbols that represent such features as streets, buildings and other structures, infrastructure (power and pipelines), streams, vegetation, and other made-made and natural features.

If you like reading maps and have experience doing so, you may find that with little to no instructions you will be able to understand most of the graphic content shown on a topographic map. For the most part, interpreting the lines, areas, and other symbols will be easy. The system of colors and line weights used will also help make the features represented more obvious. For example, areas shaded in green indicate the presence of vegetation, usually forest. Features colored in blue represent water, lines of blue represent small streams, and amorphous shapes can be lakes and ponds. You will easily understand what you are looking at, and if not, refer to the legend when in doubt. The various map features are shown as points, lines, shading, and text. The width of lines and intensity of colors graphically help to distinguish between higher and lower levels of importance, depending on the size and extent of the feature. For example, individual houses may be shown as small, uniform black squares, while the actual shapes of larger buildings are shown. In densely built-up areas, most individual buildings are omitted, and the area is shaded in light gray or perhaps standard urban land use colors. On some maps major public buildings such as post offices, churches, city halls, and other landmark buildings are outlined using a set of symbols that can be found in the legend. Features such as cemeteries, airports, and athletic facilities also follow a standard set of symbols.