Neighbors utilizing 1' of my property?

[Aaron Frances]

Hello everyone I had a survey question. I own a 2 flat in Chicago and was going over the survey of the property and the diagram reads that my property line is 1' foot in opposite direction from my fence. Which leads me to believe that my neighbors are utilizing 1' x 125' of my property for their gangway. They are a 14 unit condominium building. After reading the survey I didn't mind it thinking maybe it's a good thing so this way I have reason to be on their side of fence to service my property with a ladder if need be. But then other ideas sprang to mind. I can increase my gangway to a comfortable width? Or may I can install that 3 car garage that I've been wanting. Has anyone ever run into this? My home is an American four square ornamental that was built n 1906 and my neighbors building I'm guessing shortly after maybe in the 20,30's. By the looks of my picket fence it seems the fence may have been there since 60's or 70's.