This is simply for being in (or over) every area of the game. The first few missions in the game leading up to getting your crib should get you about 15/18 hoods uncovered. Jump in a plane found at Wesley Cutter INTL in the north part of the New Colvin district and fly around. The areas you are probally missing should be around the luchadore stronghold. The jets are very easy to control and you will be able to fly over everything in no time!
This will also unlock through normal play time pretty early. This is just a way to unlock the achievement fast if you wish to do so.