When zooming out to, e.g. all of Germany, a cgpsmapper map is drawn very fast by my eTrex. A mkgmap map takes a much longer time. Both show motorways only. Perhaps there is really less data in the zoomed out tiles?
2. Staircase lines in the outer zoom levels. This is where smoothing would be really welcome. I think (I could be wrong) that at the high zoom levels you will have to join the different parts of a road up before smoothing them (or something that has the same effect).
I'm trying this at the moment, but it destroys my map. Seems to have some bug in it. Could it be a problem with some linking of nodes to ways pointing to the original way?
3. Motoway ramps. I guess we can leave them out at outer zoom levels if it doesn't affect routing.
This is my opinion too. This should also be achieved by setting a reasonable MIN_SIZE. See below.
4. Lakes, forests at outer zoom layers. We should have a way of leaving out smaller polygon features at outer zoom levels, while leaving in the larger ones.
This should be possible already with the MIN_SIZE in SmoothingFilter. Maybe neccessary to set different values for lines and polygons. (Btw. In a previous patch I have extracted this code to a separate SizeFilter.) If you set a MIN_SIZE=1 it nearly doubles drawing speed on my etrex in the lowest zoom levels.