Well, the skip filter function works well, but there are problems with it - especially on South America. For South America geofabrik extract - the overview map gets rather large. Using higher polygon size on filter - would be the essential tool in order too keep the overview .img file to be getting too large, without nearly any visual deterioration. a) A quick (or I hope that would be quick) adaption could be to have instead: mkgmap:changeSizeFilter=? with ? being the number for the filter to be used. Even a value of 2, would have quite good effect in case of South America. (about 15% saving on the overview.img size with default style). b) A more optimal solution would be the following: mkgmap:changeSizeFilter="level:filter_strenght" so e.g. "0:12, 1:12, 3:12, 4:12, 5:10, 6:8, 7:8, 8:4, 9:2, 10:1" A filter working this way, would have great impact on the overview.img size, as well as normal map.img size - without leading to strong visual impact. (up to 50% saving on the overview.img size) The effect of the polygon size filter on South America is especially strong, as there is a huge sea area included in the extract... (also I still don't understand, why mkgmap makes so small squares for the sea, instead of larger squares - which should also save on .img size).