Topographic Maps and Compasses

Reading a Topographic Map

Whenever you’re in a remote or unfamiliar area, a topographic map and compass are a must.

Topographic maps are created from aerial photographs and reveal the contours of the land, including hills, ridges, and valleys, as well as lakes, rivers, creeks, trails, and roads.

• Contour lines show the elevation of the ground.
• Contour intervals reveal how much vertical distance there is between each contour line—closely spaced contour lines indicate very steep slopes.
• Contour lines that are sharply tapered indicate an uphill direction.
• Rounded contour lines typically indicate a downhill direction.

The Global Positioning System (GPS) is a navigation system based on a network of 24 satellites. Users with a GPS unit can determine their exact location (latitude and longitude) in any weather condition, all over the world, 24 hours a day. GPS satellites circle the earth twice a day and transmit information to Earth. GPS receivers use this information to calculate the user’s location by comparing the time a signal was transmitted by a satellite with the time it was received. The time difference tells the GPS receiver the distance from the satellite. By calculating the distances from several satellites, the receiver can determine and display the user’s location on the GPS unit. Once the user’s position is determined, a GPS unit can calculate other information—bearing, trip distance, distance to destination, sunrise and sunset times, and more. GPS receivers are accurate to within 15 meters (49 feet) on average. Certain atmospheric factors and other sources of error can affect the accuracy. Accuracy can be improved with a Differential GPS (DGPS) or WAAS (Wide Area Augmentation System). A GPS unit is a tool and should be used in conjunction with a map and compass.