I have a dataset of fire stations within an area. I would like to divide that area up into segments whereby each fire station covers a segment. This should be based on driving time. e.g. if I have 2 fire stations, fire station 1 should attend to all incidents with X segment as it will always be closer than fire station 2.
In the example below, fire station 1 = red dot and 2 = yellow dot. This is fictional, however you will see that station 2 covers a greater area to the south due to the high speed road going west from Hagworthingham.
I have around 50 stations dotted on the map. I'd like to break up their areas accordingly. I can use OSRM or GraphHopper but in reality its the theory behind how I can calculate this that I am trying to understand.