You can set up coverage areas in the game so that stations will only generate missions that require stations within the coverage area.
To set up a coverage area you go to a dispatch center and click on the edit button on the bottom. There you can tick the box “Create your own coverage area”.
Only the stations within this area will then be regarded for mission requirements when its stations generate missions. So, for example, you have 4 fire stations and 3 police stations connected to your dispatch center. If the coverage are is ticked, these stations will only generate missions that need up to 4 fire stations and up to 3 police stations and they won’t generate missions that need rescue or other stations. The coverage area also checks if you have the expansions needed for a mission.
This allows you to control what kind of missions you get in a certain area. Coverage areas are especially useful if you already have a larger number of stations in a certain region but now want to start in a different area without getting missions that are too advanced for your new region with less stations.
Please note: Stations that are not part of a coverage do count the stations that are in coverage areas for the requirements of missions they generate.