This map is measuring the land value within a county. Land values are dependent on population density. It's not surprising that Manhattan has such a high value when you consider how many folks are crammed into the island.
If you create a map that was land value divided by population density it would be much more interesting.
Exactly. This is making Dallas County look expensive, when in fact it is one of the most affordable major metro areas in the US.
The "elite Texas counties" the article refers to are really a figment of data representation. Sure, those counties have neighborhoods or small towns that are stupid expensive, but they are the exception. All of them are highly populous, though; all five dark red counties (Dallas, Tarrant, Harris, Travis, Bexar) are in the top-20 most populous counties in the US.
The data is purporting to show total property value, not land value. Thus, a residential tower with 400 units at $100,000 each and occupying five acres adds $40 million to the valuation. In contrast, a five-acre spread with a single mansion might only be worth $5 million. Thus, a county with more residential towers will have a higher aggregate value than a county with more luxury mansions, even though the former is much more affordable.
The map shows total land price in the county. It doesn't measure anything like affordability of land (which would be measured by something like price / unit area of land) or residential affordability (which would be measured by something like price / unit area of home.)
> This map is measuring the land value within a county. Land values are dependent on population density.
Not strictly, though population density is certainly a factor (and, since its total land value in each county, so is population, which -- as counties are not of uniform size -- is a separate concern from population density. And, probably more directly than either of those, Gross County Product.)
If you create a map that was land value divided by population density it would be much more interesting.