Your group of survivors doesn't have to stay holed up in one place, you don't have to fortify buildings to get by. You can still send out missions etc. Even leave the city for someplace else. Feel free to go all Mad Max on this place.
When your group is mobile, everyone travels around the map in a group marked on the map as a flag INSERT PICTURE HERE, to move the group select the flag and choose Move Group on the green postit, then select a new place to go to.
Remember, when moving the group you must have enough fuel to do so if you have any vehicles, if you have any vehicles that can't make the trip you will be asked to top up your vehicles. See VEHICLES on how to refuel.
Also, when your group is on a building, they will occupy that building and use it. Example, if your group is on a lab or workshop you will be able to RESEARCH or MANUFACTURE thing while your group is there.
At all times a group will scavenge whatever it can from the location it is at, example if your group moves to a house all the food etc will be automatically scavenged, and the zombies killed.
The rates at which you can do things on that tile depend on which people are left idle (not on a mission someplace else). See SURVIVORS for details.