I considered a subway map-like the London Tube. But decided it was probably a little too modern for what I was thinking.
So I searched street maps. I found one, also of London, and printed it as an 8 x 10, then took it to FedEx Office to get it copied as a transparency.
Years ago for the boys' room mural, I bought an overhead projector for $10 from a used office supply store-maybe a recycling place?- I found through eBay (refine your eBay search to local shops). Glad to use it again, I projected the city map on the plywood (after using woodfiller and covering with Kilz).
We taped off the roads to paint only the areas around the roads.
And those London stamps? They now show some landmarks.