That's when I break out the postal code. If your city has that much of a span, then tell Google to start at your postal code instead - the idea being that you can usually drive from one end of a postal code to the other in <5 minutes. I know there are postal codes that span long distances, but they tend not to be in cities that span long distances.

I guess I'm lucky - I'd never looked before, but I checked, and I live in a very small town, about 50 feet from where Google Maps places my town name.

I get your point - if you live in North London, then getting directions from "London" is probably not the way to go. Postcodes seem to be the quickest way, for me.