(I'm about 35-40% in now, but going back to the very beginning -- I listened to this in the car today:)
"Mr Dursley blinked and stared at the cat. It stared back. As Mr Dursley drove around the corner and up the road, he watched the cat in his mirror. It was now reading the sign that said Privet Drive -- no, looking at the sign; cats couldn't read maps or signs. Mr Dursley gave himself a little shake and put the cat out of his mind."
So you think cats can't read maps, can they, Uncle Vernon?
(And her name wasn't even Professor McGonagall ... well, not that I was ever aware, at least!)
And yes, that is a map of London, too.