alt Hacker NewsI think you're misunderstanding what they are saying. They don't use background location data, but they do use your current location data. Try the "Find My Train" demo on their site - it asks for location permission.
Or their API - it also expects device location data:
> At a minimum, requests to the detect endpoint _must_ contain a device's location measurement. Additional fields can be included where available to improve the accuracy of the returned results as outlined below.
wait - so you think that the map is made up of people who are all sitting on that website using the Find My Train demo?
I think you are missing the point - what is collecting data on all those trains.