Simplification of the topology of a mesh object Is there a way in Blender to simplify a mesh which consists of multiple triangles without removing triangles? The structure should remain the same, only a few larger ones should emerge from the many individual triangles. 
This simplified object should be used for level of detail views and from the distance only the structure should be recognizable, but no elements may be missing, as e.g. it is with the Decimate modifier is the case. Here, triangles are simply removed, which from a distance then looks like there is no element at all. Especially with an object that represents a land surface, elements are missing on the edge.
Is there any other way with Blender to create such an object?
I have found a solution. The problem was that BlenderGIS imports the shapefile incorrectly and I first have to remove several vertices (with bpy.ops.mesh.remove_doubles (threshold = 0.001). Then the decimate modifier will work,too.