One concern I have is that once an area is built up, it's not clear that there will ever be transactions of unimproved land in the area, so I don't know how we keep "unimproved value" from being anything but a fiction.
As housing fads change, some styles will go out of favor. Great rooms replace lots of small rooms.
Technology changes, too, will make some houses obsolete; older roof technology, plumbing, HVAC, inefficient systems, too little insulation and no space for more.
Houses that are obsolete for their location will sell as teardowns. In that situation, the land value is measured by the selling price plus the cost of removing the old house from the site. Assessors can work with those figures very well. Connect the dots from one to the next to the next, and the land value map shapes up.
