A bit of both. Adamstown, a new (2006) suburb of Dublin, is a very obvious example; it was planned on the basis that it was on a train line, and a station was b

A bit of both. Adamstown, a new (2006) suburb of Dublin, is a very obvious example; it was planned on the basis that it was on a train line, and a station was built as part of the initial development. Less dramatically, you tend to see densification around train and tram networks.