Change auto-lock timeout by GPS?
There are apps that disables the lock scren when you are connected to certain WiFi or when your phone cell is connected to certain tower or as per your requirement, on GPS.

I believe, but not sure, tasker can do it with GPS.

But why not use the WiFi address to disable unlock. I reckon it will be more useful than GPS.

Look at http://www.addictivetips.com/mobile/automatically-disable-android-lockscreen-when-connected-to-home-wifi/ for automatically disabling locks creen on WiFi.

Also don't forget to check llama, awesome and free location based profile management. You can do tons of stuff based on what cell tower you are connected to.