Henry George was an economist who pointed out the main problem with the economy was the concentration of ownership of LAND, and how that concentration prevented full economic development. Furthermore he pointed out most of the value of land had NOTHING to do with what a person did to the land,but the value of the land was the product of Society. The best example of this is why Gasoline Stations tend to e at traffic intersections. Why, so that people will see them and drive in to fill up. Gasoline stations are willing to pay top dollar for that location, but the value is NOT the building of the Station but the actual location.
This was the favorite saying of successful business, the three rules of a successful business is LOCATION, LOCATION, LOCATION.
George reasoned that given that location is the main factor in the value of a piece of land, why should the owner of the property get a return for that value. The owner did NOT create the value, Society did, so why should society NOT receive the value?
Before someone complains about "Property Rights" Henry George did not advocate community ownership of property, he liked private property. What Henry George advocated was that mere owner something should NOT give you the right to receive "rent" for the property. In George's view All Rental value for merely owning property should go to the community, but any value you received for the improvements should go to the person doing the improvements.
How Henry George proposed doing this was to tax land for its value without any improvements (For example high tax rate at an intersection of two highways do to the fact Gasoline Stations put a high value on such locations even without building a Gas Station). George than would NOT tax the improvements. Remember the power to tax is the power to destroy. Thus if you tax something to much people will avoid whatever is being taxed (or evade the tax but that is another issue) and slowly (or quickly depending on the tax) destroy what is being taxed.
George says there was one exception to this rule, Land. Land is hard to destroy and create. Given that fact a tax on land rarely if ever destroys what is being tax (i.e. rarely does the land get destroyed).
Thus under George's tax system, you tax the land based on its value, even if it is not being used in its most valuable way. You also do NOT tax improvements for improvements should be encouraged and the best way to DISCOURAGE improvements is to tax the improvement.
Various Municipals taxed using the Georgian Tax System, with the biggest being the City of Pittsburgh (Which ended it in 2001 for reason explained below). The reason it was adopted and used for almost 100 years was to force people to use their land for its greatest economic gain. In this it worked for many years (The City of Pittsburgh did not adopt a complete Georgian system for it had two tax rates, one on land and one on improvements. This dual system was created to keep up Tax Revenues. Under a 100% Georgian system you could have whole neighborhoods paying almost nothing in taxes (do to low valuation of the housing location) while other areas would have high tax payments (Do to very high value put on the property location).
As I said this system worked for over 100 years until the County GOP decided to "do "Property tax reform" in the late 1990s. By the time the "reform" movement had run its course, the county had been re-assessed by a new assessor who did not understand the Georgian tax system. He put a higher value on land that had buildings on the land than on vacant fields (Which undermines the whole concept of Georgian system of taxing the value of land only). This was used by local businessmen to have City Council drop the Georgian system. Many of these business men benefited from this change for the drop in the tax on land was compensated by the increase in the tax on buildings. The effect of this change was a shift of the tax burden from Business to Owner/occupiers (And all of this was done under the headlines of helping grandma keep her home, in the end she ended up paying more for her land was not worth much but her house was).
I went into the background of the Georgian tax System for it is very compatible to the concept of using eminent domain to take private property for "greater good". The Courts UPHELD the Georgian system even as it put a greater burden on Businesses than owner/occupiers. The same will occur here, all the Constitution guarantee is your land will NOT be taken WITHOUT COMPENSATION. The Constitution does not says your land will not be taken. You must be compensated based on the value of the land, but the state can take the land. This reflects the concept of Tax being the power to destroy. In the Georgian tax system the tax on land was design to raise revenue while doing minimal economic damage to the economy. The same with this use of eminent domain, it is the giving of property to greater economic gain and the Courts upheld that concept BEFORE Henry George, and followed it After George's concepts where made into law.
For More on Henry George and his tax system:
http://www.henrygeorge.org/denigris.htm