It is triggered when map state changes. After panning , zooming or map type change and also on page load. Try it. It returns an object as its single parameter. The properties of the object:
- ll: "60.170293,24.939554"
- spn: "0.043719,0.087891"
- z: 13
- t: "k"
They are lat/lng, span, zoom and map type. They are maps.google.com url parameters. If you click 'Powered by Google' logo link, those parameters are used to form the url.
You can use those for similar linking purpose, or you could store those in a cookie. A back button could also be constructed using the event.
The event is most convenient for fetching marker data from a server. Center lat/lng and span are just the parameters needed and the event is triggered just when needed.