Fun with Google Maps. New map is very helpful. You can type in any address, and it shows you the closest train station(s). It doesn’t measure the distance, unfortunately. However, it also allows you to enter two locations, and it will show you the subway route between the two points (something you can also do on the MBTA’s website, but without the visual aid), and you can also enter two subway stations & see how to get from one to the other.