Pit People

Simply complete 15 mission only found on the world map. (Not through the city quest selection) you'll have to return to the city once all 15 are done. And these have to be completed in a single area, open your map up to see the name of the area your in. You'll sometimes switch to a new area when returning to the city, but you can get back to the area you were completing missions in simply by leaving and re-entering the city until your back to the area you want. If you've been completing world map missions before the update that brought this achievement, missions you've completed before will not count and you may not have enough new added missions to get the achievement. If this is the case just start a new file, skip the prologue, and get to work. I personally had to do this.