Lee Swordy says it best so let me quote from his AF2 Manual:

"7. FSUIPC
AFCAD can be used by itself for most airport design work but placing taxiways and parking around buildings and structures can be awkward, as building are not currently displayed on AFCAD. This makes it especially difficult to mate gate parking spots with terminal boarding bridges. For that kind of work it is preferable to link AFCAD with Flight Simulator using FSUIPC. You can start Flight Simulator and ‘slew’ around an airport in a virtual aircraft and crosshairs will move on the AFCAD map to show your location. Alternatively the AFCAD map can be locked to your aircraft position like a moving map display. FSUIPC is an add-on program that, among its other uses, allows third party software to interface with Flight Simulator.

FSUIPC does not come with AFCAD but it can be downloaded from the following site:"

May I suggest placing the AF2 Readme File ("C(x):\Program Files\afcad221\ReadMe.htm") on your desktop for quick reference.