The majority of new stations get built in purpose designed "transit oriented development" e.g. where housing and amenities for 10k+ residents are built at one point in time.

Major Boston examples include the Seaport District and Assembly Square.

Seaport: http://www.bostonplans.org/projects/development-projects/sea...

Assembly Square: https://en.wikipedia.org/wiki/Assembly_Square#Marketplace_hi...