How to read and use a topographic map in a survival situation.
Use of a topographic map in a survival situation
Topographic maps describe the shape of the land and can be used (along with a compass) to help you locate natural and man-made features like woodlands, waterways, important buildings, and bridges. The information derived from a topographic map can help you locate sources for water and even if a clearly-defined water resource is not visible on the map, you can use the topographic map, which illustrates the elevation of the land, to locate low-lying areas where water may collect. Topographic maps can also help you locate the most appropriate shelter for your particular survival situation or plan potential escape routes when needed.
Topo map contour lines
Topographic maps also show the distance between two places and the direction from one point to another. On a topographic map, the topography of the land is shown by contours or imaginary lines that follow the ground surface at a constant elevation. Contour lines that are close together represent steeper slopes while areas on the map with widely-spaced or no contour lines represent flat ground. Often times the contour line will have a numeric value, indicating the elevation in feet, embedded on the line. In effect, the topographic map takes a three-dimensional landscape and represents its shape on a two-dimensional map using the contour lines.
Another set of lines (usually dashed) are used to illustrate a grid system on a topographic map. This grid system represents the globe’s east-west measurements, or longitude, and its north-south measurements, or latitude. These lines will be less important than contour lines in helping you navigate your terrain, but if you need to report your position to a search and rescue team, they will help you correctly report your location.
Colors on a topographic map
Colors on the topographic map are used to indicate other features. Woodlands, forested areas, or areas with significant vegetation are tinted green. Waterways (rivers, lakes, waterfalls) are colored blue and can contain additional symbols pointing out specific characteristics of the body of water. For instance, a single dash on a blue line indicates a waterfall while a double-dash on a blue line indicates rapidly flowing water in a small stream. Similarly, an asterisk symbol inside a blue shaded area is used to indicate a rock or other hidden object located beneath the surface of the water.
Buildings may be shown as black squares, outlines, or unique symbols indicating the type of building. It is not uncommon for topographic maps to contain special symbols indicating the location of cemeteries, fire stations, hospitals, and schools.
Recent changes in an area may be shown by a purple overprint while roads are printed in red (major roads) or black (minor roads) solid or dashed lines, depending on the road’s size and surface construction. White can have various meanings on a topographic map such as permanent snowfields or areas without significant forest or water features.
Scales and measurements on a topo map
The margins of the topographic map will typically include a scale, which provides information about the ratio between measurements on the map and the landscape’s actual measurements (e.g. one inch may represent one mile). A common scale on topographic maps is 1:24,000 which roughly corresponds to 2 1/2 inches to the mile. Topographic maps with a larger ratio, such as 1:100,000, will provide less detail about the immediate area but may be helpful in mapping a route over greater distances.
Below is a sample table of symbols used on topographic maps. United States topographic maps can be downloaded from the USGS.
Here is another sample table (more compressed) of symbols commonly used on topographic maps.