Hi Gerd I'm having trouble building GB with low-res-opt (+updated shapeSplitter), my style and options getting this error: Exception in thread "main" java.lang.AssertionError at uk.me.parabola.mkgmap.filters.ShapeMergeFilter.addWithConnectedHoles(Sh apeMergeFilter.java:352) at uk.me.parabola.mkgmap.filters.ShapeMergeFilter.tryMerge(ShapeMergeFilte r.java:252) at uk.me.parabola.mkgmap.filters.ShapeMergeFilter.mergeSimilar(ShapeMergeF ilter.java:147) at uk.me.parabola.mkgmap.filters.ShapeMergeFilter.merge(ShapeMergeFilter.j ava:99) at uk.me.parabola.mkgmap.build.MapBuilder.makeSubdivision(MapBuilder.java: 940) at uk.me.parabola.mkgmap.build.MapBuilder.makeMapAreas(MapBuilder.java:838 ) at uk.me.parabola.mkgmap.build.MapBuilder.makeMap(MapBuilder.java:333) at uk.me.parabola.mkgmap.main.MapMaker.makeMap(MapMaker.java:114) at uk.me.parabola.mkgmap.main.MapMaker.makeMap(MapMaker.java:70) at uk.me.parabola.mkgmap.main.Main.lambda$processFilename$1(Main.java:290) at java.util.concurrent.FutureTask.run(FutureTask.java:266) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.ja va:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.j ava:617) at java.lang.Thread.run(Thread.java:745) and quite a few tiles empty, but the matching ovm_ are generated. I'll try and reproduce in simpler environment. Ticker