Have you ever used Google Local to find something in your own neighborhood?
I don't know how the heck they have collected and organized all that data!
If you select 'View Larger Map', you get a map as big as your window and screen can handle (which is big in the case of my Apple 30-inch screen), and if you zoom in to max, you'll be amazed at the detail. I almost expect that if I put in a new flower bed in the garden, it will be on the map tomorrow.
Not to mention of course that they can find all the local businesses somehow.
I don't know which countries they have covered so far, but it works fine for UK, you just replace .com with .co.uk