Are you always connected to Internet ?

The answer is often no. No network, bad speed. It can be useful to use a web browser without network. Google's answer to this problem is Gears. In MapFish, you can use this technology to work with your data in an offline mode. You define an area of interest, cache the data with Gears and then you can remove the network cable and continue the navigation. It is also possible to offline edit the data and when you are again online, to do the synchronization procedure.