When I'm not working on children's books my "day job" is creating illustrated maps. Here is a step-by-step of one I did for Westchester Magazine.
First is the scrap that the client sent-- rough map info and a few reference photos of some of the buildings. The yellow box lists all of the places that need to be included. ("Yikes!" I say to myself. "How am I gonna make that look pretty?")
Here is a very-cleaned-up version of the sketch after the client approved it, with corrections indicated:
And, voilà, the finish!