Hi Steve,
Tiles that would contain a land border need to be further split along that border. This could be done 1. Directly by splitter 2. By running mkgmap once for each country. 3. Some intermediate process.
I believe it would be best in the long term for splitter to make the split, but perhaps the other strategies could be used temporarily in order to concentrate on other parts of the process.
Up to now I see no need to change splitter. We already have the UnusedElementsRemoverHook, I would try to add a similar method to filter data which is outside of a given polygon. Depending on the complexity of the polygon this can be quite time consuming for just on tile. If we try to do that in splitter and try to split e.g. Europe, we have to store a lot of complex polygons as we try to process many tiles at once. I see only one possible advantage when doing it in splitter: A perfect algo would be able to make sure that all tiles for one country have a similar number of nodes. When we use mkgmap for filtering a single rectangular tile might just overlap a country in a very small area, thus the resulting *.img would be very small. Gerd