Huge zone was marked as "agricultural use" compared to previous map standard where much smaller grid sections where designed for agricultural use. This large section required huge amounts of modification to make it correctly fit in the correct areas to avoid overlaps in the nearby urban area/etc. In the end it is easier to delete it and correctly assign new agricultural zones instead of moving every side of it. Regarding the buildings deleted, these often had incorrect dimensions or locations: it's easier to redo them.