Assessments that favor the big landholders

It is apparently standard practice for assessors in some places to value large parcels of land very generously.  I'm not talking about special valuations for farms or forests (even if they are long-fallow and in areas where land sells for hundreds of thousands of dollars per acre).  Rather, I am talking about valuations which treat the portion of an owner's land beyond the minimum zoning size as if it were worth perhaps 10% of its real value.

This happens in fairly dense suburban neighborhoods and in places where much larger lots are the minimum.