Comment 2 for bug 579472

When using OSN, it firstly displays tiles that were previously stored in the cache (sdcard).
If not, it tries to download the tile over internet.
The problem is when connection is flacky or inexistant, the map stays blank.

So, when requesting tiles over internet,
if tiles at zoom+1 or zoom-1 are available we should use them and firstly display them using extrapolation, even it's not very accurate, it's obviously better than a blank one.
Then, if tiles are correctly downloaded we could display them.