Boston.com has created an interactive Google Maps for this year's Boston Marathon, which is useful both for participants and those who want to watch. More info about pdf vector format of a Free vector map USA, Adobe illustrator can be found here.
Spectators can use the Boston Marathon Map to find the best places to watch the race anywhere along the course. If you select a mile marker on the map you can view suggested locations to watch the marathon nearby.
Participants in the race can use the map to explore the route. Each mile marker on the map includes details on the expected arrival times, the course elevation and the net change in elevation from the last marker. One really handy option is to enter your hoped for time for completing the marathon and then view the time you should aim to arrive at each mile marker. Source