Julia J. Quinlan 
Keys, Legends, and Symbols in Maps [PDF ebook] 

Just as maps help us find our way around unfamiliar places, keys and legends help us navigate unfamiliar maps. This helpful volume uses clear, easy-to-follow text to teach kids how to use a map’s legend or key to figure out what the symbols on it mean. It presents commonly used symbols, such as the stars showing capital cities. The book also explains how certain types of maps, such as USGS topographic maps, employ standardized sets of symbols.