I found two conflicting statements regarding the limit usage of google stati map api
According to this link, 25 000 usage limit are allowed per day
According to
25000 is the limit per site, 1000 is the limit per viewer. Site is tracked by URL or developer key. Viewer is tracked by ip address. My browser loading your page would count 1 against your site limit, and 1 against my ip address viewer limit.
To get an API key, you can apply here: https://code.google.com/apis/console/