[ascorbic]

Unsurprisingly they mostly run trains to places where people live, but there is some influence the other way too. New commuter rail lines have historically lead to more development around the stations (e.g. Metro-land 100 years ago https://en.wikipedia.org/wiki/Metro-land), and in cases where a station is built for reasons other than there being a centre of population (e.g. because it's an important junction) then that does also tend to lead to houses being built. Of course in more recent times this hasn't happened because you can hardly ever build outside of existing conurbations, but that is changing and several new towns are being planned for new or existing train stations.