Map of Springfield

Here is the full-size map (pdf version here). Some more info:

While the placement of most locations is arbitrary, many are placed according to where they appear in relationship to each other in specific episodes of The Simpsons. In some cases ‘one-time references’ to specific locations have been disregarded in favor of others more often repeated. Due to the many inconsistencies among episodes, the map will never be completely accurate.

(Link from Information Aesthetics blog.)