[mkgmap-dev] what do the 0x4a polygon in the mean?

Hi experts, today I played with a map that has non-rectangular shape. I tried this: Use the dem-poly option to cut also the 0x4b polygon for each tile, use these 0x4b polygons also in the overview map and also for 0x4a in the overview map. I expected that this would create nicer maps but found no effect in MapSource. I tried this with the sample from Andrzej. The DEM data in the Winterkarte does not show the steps which are produced by mkgmap at polygon boundary. What am I doing wrong? Gerd