Terraforming Broken?

[SabaothMastema]

I'm trying to to terraform my sim so that it's as flat as possible. However, certain simply won't lower or work so to speak.

I have peaks that I can effect at all and other spots that are simply unaffected by the terraforming tool. What could be the issue? How can I fix it?

 

P.S.

This isn't my first terraforming, I generally know the basics.

[Mollymews]

regions have an underlying height map

to see the region height map as it affects your parcel then use the Revert option of the Edit Terrain tool

on a standard mainland region the terrain can only be raised or lowered up to 4 metres above or below the height map at every given point

so if say on one side of your parcel the heightmap is at 20 metres then that side can be in the range 16 to 24. When the other side is at say heightmap 10 metres then the range is 6 to 14 metes, so the whole parcel can never be totally flat