You can access specializations in the Specialization tab of your fire stations, allowing you to designate fire stations as rural or urban.

All fire missions are flagged as either rural, urban, or both. If the rural specialization is active, the station will only generate rural missions. If the urban specialization is active, it will only generate urban missions. Stations that don’t have these specializations active can generate both rural and urban missions.

Rural stations have a larger mission generation radius.