What's the API Key for in Google Maps API V3?
Whilst it is true that V3 of the Google Maps API does not require an API key, it is there for a reason. Google recently introduced the following usage limits:
Web sites and applications using each of the Maps API may at no cost generate:
- up to 25,000 map loads per day for each API
- up to 2,500 map loads per day that have been modified using the Styled Maps feature
In order to monitor usage an API key is necessary, as the developer notes make clear:
All Maps API applications should load the Maps API using an API key. Using an API key enables you to monitor your application's Maps API usage, and ensures that Google can contact you about your application if necessary. If your application's Maps API usage by exceeds the Usage Limits, you must load the Maps API using an API key in order to purchase additional quota.
So whilst you don't need to have an API key it is useful if you want to monitor your usage and also required if you buy additional usage quota.
V3 of the Google Maps API does not require an API key. So you're good to go.
Edit: In the time since I answered this question Google released support for API keys in v3, letting you see usage of your API site in Google's developer console. The original answer is still accurate: API keys are not required, but they are now recommended.
As of June 22, 2016 Google Maps V3 no longer supports keyless access so you need to get a key for every (referrer-)domain which has never had a Google Map on it before.
Get your key here: https://developers.google.com/maps/documentation/javascript/get-api-key
and append it to the URL of the script like so:
<script src="https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY" type="text/javascript"></script>
If you do not provide an API key you will see this warning instead of your rendered map:
and your browser's console will tell you the reason:
Google Maps API error: MissingKeyMapError https://developers.google.com/maps/documentation/javascript/error-messages#missing-key-map-error