When you look at a topographical map, the first thing you notice are an abundance of small lines in various patterns. These lines mark where a specific elevation appears in an area. Surveyors established this information by crawling over every square yard of land in the U.S. and compared their findings with aerial stereoscopic photos. It's funny to think about, no matter where you go, someone's been there before.
To comprehend these lines, imagine that the earth flooded, that the sea levels rose 1,000 feet. Look for a line that says 1,000. All the lines that are marked with 1,000 show what the new coastlines would look like. If you are located in, say, New York State, you'll find a bunch of islands. In Florida, nothing but ocean. In Colorado, it may remain unchanged. If you imagine these lines to be watermarks, you'll quickly be able to imagine how the terrain would appear if you were there. To help visualize things more quickly, compare a topo map to an aerial photo of the same area. This will help you recognize that the closer together the lines are, the steeper the inclines will be, and help you guess the difference between a rise and a pit when the elevation is not indicated.
Remember, the government made these maps for military reasons. the same is true of GPS and avalanche beacons.
