Topographic Maps
For wilderness travel, don't plan to use just any old map. Put away the highway maps you buy at the local supermarket; they are great for getting you to the trailhead but nearly useless once you are actually on the trail. What you want is a type of map called a topographic map. A "topo" map not only shows shows natural and man-made features, it also displays the physical shape of the terrain. This is done by way of "countour lines" that show the geometries of constant elevation of the land. Lines that are close together represent steep slopes. Lines that are widely spaced are gentle slopes. By studying the shapes of the contour lines you can determine much information about the land. For example, mountain peaks are represented by contour lines in concentric rings. V-shaped lines pointing uphill indicate a canyon or gulley. V- or U-shaped lines that point downhill indicate a ridge.
Topo maps are produced by various government agencies and some private organizations. The most comprehensive source is the US Geological Survey (USGS). They have mapped the entire United States at various scales. The most popular scale for hikers is known as the 7.5 minute series because each map covers 7.5 minutes of latitude by 7.5 minutes of longitude. The scale for these maps is 1:24,000, so 1 inch = 2000 feet. These are known as "large scale" maps, because each map covers an area less than 10 miles by 10 miles in great detail. The USGS also produces topo maps at several smaller scales, primarily 1:100,000 and 1:250,000. These show larger areas but less detail than the 7.5 minute series. Previously, the USGS produced a series of 15-minute maps, but these are now discontinued except for Alaska. The scale of these maps was 1:62,500, where 1 inch = not quite 1 mile. (Not until Alaska did they use the more logical scale of 1:63,360, in which 1 inch = exactly 1 mile!) This was a very convenient scale for hikers, and several private companies sell updated versions of the old 15-minute maps for popular hiking areas. Remember that USGS maps are often 10 or more years old, so don't depend on them in areas that have seen recent development.
The US Bureau of Land Management also produces topo maps for many BLM lands. These tend to be small scale maps of limited use for hikers. In many states, certain state organizations produce specialized topo maps. In California, for example, the Department of Parks and Recreation produces individual topo maps for many state parks. These are usually based on USGS 7.5 minute maps.
Once you have a topo map, learn how to read it. The USGS produces a free pamphlet entitled "Topographic Map Symbols. Click here to link to their on-line version (use your browser's BACK button to return to this page).You should also pick up a good book on the subject, such as Outdoor Navigation with GPS.
One thing you often need to do with a map is read the coordinates of a particular location in terms of either latitude/longitude or UTM. (Check Outdoor Navigation with GPS for a complete discussion of the UTM system, or click here for an on-line tutorial.) It is easier to do this with either a latitude/longitude ruler or UTM roamer. You can print your own tool that includes both latitude/longitude and UTM scales for 7.5 minute maps, as well as several other useful scales by clicking here. Print the .pdf file on clear transparency material and cut to size (depending on your printer and transparency material the final scale might be close but not exact). You may print copies for your own personal use but may not print copies for resale without prior written permission from Annadel Press.
To use the tool, you need to prepare your map. To use the latitude/longitude scales, look for the 2.5 minute tick marks along the map vertical and horizontal neatlines (i.e. map borders) and use a ruler to connect the marks. Be sure to extend the vertical lines to the very edge of the page, not just the map boundary. You will end up with something that looks like a tic-tac-toe board. To read the latitude of a particular location, align the ends of the scale with the appropriate 2.5 minute lines and read the incremental latitude of the location. Be sure to use the correct version of the scale. If the 2.5 minute lines are on even minutes, use the scale readout begining with 0. If they are on 30 second increments, use the readout begining with 30. Add this incremental number to the absolute latitude of the lower 2.5 minute line. Read longitude similarly, except that you will need to angle the ruler so that both ends line up on the 2.5 minute longitude lines. This is necessary because the distance between lines of longitude decreases as you move northward but the distance between lines of latitude remain constant.
To use the UTM scale you must first prepare your map by drawing lines to connect the blue UTM easting and northing marks on the map neatlines. You then place the target location of the UTM scale on the location of interest and read the incremental UTM values on the nearest easting and northing lines. Once you understand the UTM system, it is much easier to use in the field than latitude/longitude, so you should spend a little time to learn it if you have the chance. One way to gauge the experience level of a backcountry navigator is whether or not they use UTM for navigation.
