The film doesn't tend to use maps to speak of the city's division into zones, though here Major Calloway is pointing to the International Zone as a possible meeting place with Harry Lime. 
The broad lines marking out the divisions of the city on this map are a recurrent backdrop to encounters in this room, even when the lighting shifts  into noir mode:

There are other maps in Major Calloway's office, and also in the Russian Liaison Officer's room across the corridor: