It is almost impossible to get lost in the Keys as U.S. 1 is the only road that travels continuously from island to island. All roads intersecting with U.S. 1 either come to a dead end or bring you back to U.S. 1. When you're in the Keys you will notice little green mile-marker signs (M.M.). The best way to get around the islands is to know the mile marker of your destination. The Keys begin at M.M. 113 and end in Key West with M.M. 0. Think of these mile-markers as addresses and they will help you find your way around in the Keys.
Below is a mile-marker guide for quick reference
City