How to convert a specific multipolygon to minimum polygons

Question

I've got this kml file with one multipolygon inside.

A link for the file are here

multipolygon.zip

My goal is to get a multipolygon with the minimum count of polygons with only outer border and some holes or island. I'm not a profi in gis programs, i tried the last three days a lot of tools in qgis but with no success. I get every time a single polygon with all these small borders. Who can help me to reach my goal?

Answer 1

Here is an approach I would try: First explode the multipolygon into a a set of single features. (In QGIS that's under the Vector->Geometry Tools->Single part to Multipart) Then import the polygons into a spatial database such as Spatialite, and run a query that searches for polygons that do not touch any other. In general you would write a query that compares the polygon table against itself, something like:

SELECT p1.id
FROM polys p1, polys p2
WHERE p1.id <> p2.id AND
ST_Touches(p1.geometry, p2.geometry)=0;