Dear Maning,
Unless your map extract is a perfect island, you may have to move the coastline endpoints to make mkgmap happy. I think it is, the Philippines is an island/archipelagic country:
What matters is the map extract that you are using. If it contains half-cut islands from, say, Indonesia, then mkgmap may have problems with that.
coastline generation for Finland, I both adjusted the Geofabrik cutting polygon (it took a few iterations with Frederik Ramm) and moved the endpoints of the mainland coastline to the tile boundaries Do you mean using splitter? I am not using splitter at the moment since the data is small enough as one img.
No, I mean the map extract that I can download from http://download.geofabrik.de/osm/europe/. To my knowledge, it is cut by Osmosis, using a cutting polygon. I requested the polygon from Frederik and adjusted it a little, so that all of the Finnish administrative boundary was included in the extract and all lake multipolygons near the border were intact. I do use splitter to split the map extract further (currently into 6 tiles), but that is a separate issue. Marko