The sea generator of course adds the sea area with multiple polygons and also adds the land area with multiple polygons. They are used only if you have an according rule in the style. I don't see a chance to change anything here.
I agree. Sorry, I did not want to say that this should be changed.
The question is why the highwayCount is > 1. I have searched where the highwayCount is increased. Some places are quite understandable but two are conspicuous:
Osm5XmlHandler.startInNode checks for a tag mkgmap:on-boundary. If that is set the highwayCount is increased. So far so good but this is not performed in the PBF and o5m handler. So maybe this can be removed or must be added to the other handlers too.
The base class OsmHandler has a method addCoordToWay(..). In this method the highwayCount is increased always - no matter if it is a way or not. This was introduced by merging the way-closing branch. So Steve should have a look on it. I think that's not intended.
yes, I think so as well. I don't fully understand what the removeShortArcsByMergingNodes() should do with coast line data and I don't know why the PreserveHorizontalAndVerticalLinesFilter() is needed. Maybe we can omit these routines for ways that were created by the sea generator. Gerd