问题:

Ok, Google Maps API V2 needs a key and V3 doesn't. My question is exactly why is that? What was the key for? And why did they take it away in V3?

回答1:

My theory for why they required a key in V2 was so that they could guarantee that you had agreed to the terms of use. Per their lawyers. Then for V3, the Google developers decided not to have a key because it is a pain that really doesn't guarantee anything. So in the disagreement between the developers and the lawyers, the developers won. Google is one of the few companies where that could happen.

回答2:

Google Maps API V3 makes a distinction between normal users and "premium" users. You still need a key to access the premium features of Google Maps, but the basic stuff is now available to everyone without a key.

回答3:

Also, with V2 it was a bit of pain when you needed a separate API key if you were developing on your local machine and you wanted to test your website on localhost. Now there is no key required, so no more hassle with two keys.