Can I get HTML5 location-awareness to trigger an action?

Question

Here is the thing. I want to create a webapp that make use of the location awareness feature of HTML5.

I want it to survey the users location and trigger some action when he reach a certain destination (play a video, show some information, load another page).

I have started with this:

http://mobile.tutsplus.com/tutorials/html5/html5-apps-positioning-with-geolocation/

("watchPosition and clearWatch APIs”)

Now, I want to expand that, so it trigger some event when the user move into a certain areas, defined by geo-coordinates, say let the browser go to New york times page when entering Central Park.

Any ideas?