If you are going out on a well-marked trail or to an area that you know, you might be able to get along fine without a map or a GPS unit. In those cases, you may only use a map for planning or reviewing where you went. If you are trying to find a specific site, such as an old mining community, a map and a GPS unit can be very helpful. Even if you don’t take a map with you in the field, a map is still useful for planning and documenting what you find.
There are three basic levels of maps for planning a backcountry adventure:
For the big picture you can start with a Delorme Atlas & Gazetteer (or equivalent). This type of atlas shows towns, roads, rail lines, land ownership, landmarks and land features.
As you zero in on your planning, the next level of map is a 1:100,000 scale topographical map. (1:100,000 scale means that one inch on the map equals 100,000 inches on the ground.) These maps are published by the USGS or the BLM. The BLM version, if available for your area, shows land ownership (private, state, federal, and tribal). A map showing ownership will minimize your chances of trespassing (see the post, Trespassing or Where Can You Wander).
The National Forest Service offers an equivalent map at a scale of 1:126,720 (1/2 inch = 1 mile) for National Forest areas. Like the BLM maps they too show land ownership.
For actual use in the field or to use for recording a location, the 7.5 Minute USGS topographical map (1:24,000 scale) offers the most detail. These maps cover 7.5 minutes of latitude by 7.5 minutes of longitude. Even though the roads may not be as accurate as you would like them to be (see the post, Leaving the Pavement), they are a good place to start as they have land features, topography, elevations and coordinates.
Most maps are available in paper and electronic versions. You can buy maps from map stores, outdoor stores, directly from the agency that issues them, and on the Internet. There are even free maps available on the Internet. However, if you are going to be using a map frequently, you might find it more convenient to own the map.