In terms of data, we exclude everything that doesn't lie within the rectangle between points N-W and S-E.
This means defining an area which is large enough to include the surrounding villages affected by commuter traffic, train stations, and so on,
And at the same time, an area which is small enough not to find 10,000 hits in France when a customer searches for the word "station".
... basically, you need to frame your users' "mobility zone" in a way that's neither too large nor too small! 😉

A simple way to obtain GPS coordinates is to use Google Maps: right-click on the map to copy/paste the point's coordinates.