Clean polygon geometry

Cleaning a polygon geometry has two purposes:

1. get rid of unexpected lines in the visualsiation of polygon items in map views, often due to coordinate conversions.

2. remove double coordinates to finish simplifying your geometry.

Cleaning a polygon geometry can be configured with the partitioned_union_polygon (dissolve by attribute) function, see example:

attribute<LatLong_mdegrees> Geometry_mdegrees_clean (polygon, domain) := 
   partitioned_union_polygon(Geometry_mdegrees, id(domain));