This map of the Virgin Islands is an excellent asset for many reasons. I like it because it gives you a context as to where Tortola is within the West Indies. You also get an idea of how big the island is compared to some of the neighboring islands.
I especially like using this map or just the BVI map for checking out where I'm going to visit. Most of the time I try to spend at least one day exploring an island other than Tortola. Taking the ferry for a day trip to Virgin Gorda is always a blast. I also like to use this map to find some of the smaller islands by boat.
There are a few more maps that you should have a look at including: the hotels map the beaches map, and the BVI map.