How to Use a Topographic Map

How to Use a Topographic Map
Being able to read a topographical map (one that depicts the shape of the Earth's surface) means you will have the knowledge to navigate a world of off-trail areas and backcountry wilderness. Using a topographical map is indispensable even in this age of technologically savvy GPS. Properly using topo maps, as they are called, can help you plan a trip and navigate during one without relying on technology that may not always work.


Difficulty: Moderately Challenging

Step 1
Find coordinates on a map by learning how the earth is divided. The earth is divided into 360 degrees, because it is spherical. Longitude is measured 180 degrees east and 180 degrees west of the meridian in Greenwich, England. Latitude is measured 90 degrees north and 90 degrees south from the Equator. Each degree is divided into 60 units called minutes and each minute is divided into 60 seconds. By using this grid system, each place on the planet has a specific set of coordinates on the map's gridlines. Most topo maps are 7.5-minute maps, which means they cover an area that is 7.5 minutes of latitude by 7.5 minutes of longitude.
Step 2
Learn to read contour lines. These are what show the land's topography. These lines, which you will see all over the map, represent certain elevations above sea level. A contour interval is the difference of elevation between two contour lines. On 7.5-minute maps, 40 vertical feet is the usual contour interval, and on 15-minute maps, 80 vertical feet is the usual contour interval. If a trail is crossing lines that are steadily increasing in interval, then you know the trail is gaining elevation. These lines will also show features of the land, such as cliffs, slopes, ravines, valleys, mesas, summits, passes or ridges.
Step 3
Read colors on a topographical map carefully and learn them well to know what kind of terrain you might be heading into. Red lines are major roads; blue lines can represent water, such as rivers, lakes, springs, waterfalls or ice; black lines are trails or small roads; green represents forest or partial vegetation, depending on the darkness of the color; white-and-blue contour lines usually represent a glacier or snowfield; white-and-brown contour lines represent dry, rocky area; brown lines are the contour lines, and purple are any revisions on a map.
Step 4
Relate your surroundings to the map's features as you go, even if you think you are on the right route or on a trail that seems to be going in the right direction. The more features that match up where you are in real life and on the map will ensure that you are on the right track and will help keep you from losing your way. This is also important if you will be passing through this same way on a return. Things might look different going the opposite way; by taking note of several prominent features along the way, it will be easier for you to route find when you are going back.
Step 5
Find the right topo map for your area. Although these kinds of maps are produced by some private companies, the most common in the United States are those made by the U.S. Geological Survey. Most are at a scale of 1:24,000, which means one unit of measure on the map is equal to 24,000 units of the same measure on the earth. Alaska is an exception. Maps made for this area are in 1:63,360 scale. Be aware of any scale changes so that your distance and size estimates are in check.

Article Written By Naomi Judd

Naomi M. Judd is a naturalist, artist and writer. Her work has been published in various literary journals, newspapers and websites. Judd holds a self-designed Bachelor of Arts in adventure writing from Plymouth State University and is earning a Master of Fine Arts in creative writing from the University of Southern Maine.

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