Hi WanMil, Have you looked at merging adjacent multipolygons? There was some controversy on the Finnish forum <http:// forum.openstreetmap.org/viewforum.php?id=15> but I was not alone with the opinion that lakes should be defined as multipolygons, no matter how complex they are, and that large map objects can or should be split to avoid problems with tools. Ways can have at most 2000 points, for instance, and rendering tools can merge them as needed. Currently, Osmarender is flooding Kuopio, even though I did split Lake Saimaa into rather manageable chunks. I guess I should split it further, if the Osmarender bug cannot be fixed easily. But I do not dare to do it now given the strong opposition from one mapper. I think I devised a reasonable means of identifying artificial cuts between multipolygons, which I also applied to the large multipolygons that I defined, in http://www.openstreetmap.org/browse/changeset/3926233 My artificial cuts are untagged lines that are shared between adjacent multipolygons in role=outer, such as this one between Heposelkä (a section of Lake Saimaa) and the rest of the lake: http://www.openstreetmap.org/browse/way/50841967 Note that the browse window currently shows the main lake as inverted, even though the data appears to be OK in JOSM. Osmarender is having trouble with this small multipolygon too, rendering square-shaped blocks of water where the coastline should be. Best regards, Marko