Free GM Resource: The Map of Early London
The Map of Early Modern London is a bit of a work in progress, but it has improved much since I first became aware of it. Basically this is an online copy of the Civitas Londinum, AKA The Agas Map, a woodcut map of London made in 1561. The really cool thing about this historical map is that because it is a digital map, the folks behind this project are able to overlay a bunch of cool information onto the map.
You can choose to highlight specific neighborhoods or all the guildhalls. Want to look up all the known taverns? Just a few clicks and you are there. You can kind of look at things in reverse as well. Click on a spot on the map and you'll be told what is there and be given a list of historical references for that location.
Now for a lot of folks, this is just something fun to poke around with, but I could see this as a real boon to GMs trying to get their head around a large urban location in their campaign. Being able to see how things are laid out can help give some ideas. Heck, you could probably use this map as a major location in your game and use this online version to help flush things out some. Change a few names here & there and depending on how you lay it out for your group they might be none the wiser....
I think the Map of Early London can be a valuable resource and even if it isn't, for you, it could be a fun historical diversion.