Hi Marko and others, the patch for the mp code does not remove any tags from the source polygons and lines. Instead it tags all mp-source lines and polygons with mkgmap:mp_source=yes. All artificially created polygons during the mp processing are tagged with mkgmap:mp_created=yes. Example: Polygon A - natural=water, role=outer Polygon B - landuse=grass, role=inner Result after mp processing Polygon A - natural=water, role=outer, mkgmap:mp_source=yes Polygon B - landuse=grass, role=inner, mkgmap:mp_source=yes Polygon A1 - natural=water, mkgmap:mp_created=yes Polygon A2 - natural=water, mkgmap:mp_created=yes Polygon B1 - landuse=grass, mkgmap:mp_created=yes Maybe you could play a bit with this and post any new ideas how to improve the tag handling in the mp code. WanMil