QGraphicsGeoMap heap requirements exceed symbian default

QGraphicsGeoMap limits its internal use of memory for tile caching to 2 * 5MB on symbian, maemo5 and other mobile plattforms. The default heap limit of qt symbian applications is 4MB which isn't sufficient if the map tries to buffer up to 10MB of data.

The developer might not be aware of this as this isn't documented and the result is that the phone randomly starts complaining about low memory and requests the user to close applications.

This definitely needs proper documentation and might also require some explicit testing of the heap limits to e.g. prevent successful compilation with insufficient heap space.