The importance of land is often not the land by itself, but the fact that something valuable can be done to the land or something valuable can be built on the land. It is important that people be able to get title to land in order to make such improvements or to build such buildings without fear that those improvements or those buildings will be taken away. John Locke makes that argument in section 34 of 2d Treatise on Government: “Of Civil Government” (in Chapter V "Of Property"):

God gave the world to men in common; but since he gave it them for their benefit, and the greatest conveniences of life they were capable to draw from it, it cannot be supposed he meant it should always remain common and uncultivated. He gave it to the use of the industrious and rational, (and labour was to be his title to it;) not to the fancy or covetousness of the quarrelsome and contentious. He that had as good left for his improvement, as was already taken up, needed not complain, ought not to meddle with what was already improved by another’s labour: if he did, it is plain he desired the benefit of another’s pains, which he had no right to, and not the ground which God had given him in common with others to labour on, and whereof there was as good left, as that already possessed, and more than he knew what to do with, or his industry could reach to.

I have several miscellaneous thoughts about this:

1. Hernando de Soto became famous for talking about how important giving slum-dwellers title to the land they live on can be for economic development. When this advice is followed, it is an interesting example of "squatters" usurping land title when the land was mostly unimproved, and then being given land title after building a shack on a (small) piece of land. 

2. Often what stands in the way of building is not the difficulty of getting standard legal title to a piece of land, but the political monopoly over how a piece of land may be used that local governments have. If a local government holds sway over too large an area, the urge to stifle competition and fear of congestion can often lead to a political failure—and political obstruction in the way—of delivering on the social justice imperative I enunciate in "Building Up With Grace" that every substantial city have a district with essentially no height limits and excellent bus service to the rest of the city, so that people of modest means can afford to move to attractive cities—cities that work, cities that have jobs and amenities. 

3. In the modern world, very often, a great part of the value of a piece of land has to do with the other buildings and streets that it is near. One of the themes of "Density is Destiny" is about cities as the key element of a socially increasing-returns-to-scale technology. If it were possible to create more cities that work, cities that have jobs and amenities, on land that is now far enough away from other things that it is inexpensive, that would be great. Overall, great cities are underprovided. Part of the answer is letting existing attractive cities grow more; but ideally (and this is not excuse for those existing cities not to grow), it would be good to also have new, attractive cities arise. Here, I think there is an externality. If someone made a wonderful city come into being, shehe would capture only a small share of the value generated. 

4. One case in which it is easier to get a city to arise is when that city has a significantly better legal structure than the surrounding cities. Think Shenzhen. This is Paul Romer's idea of a charter city. In addition to the value of a charter city in helping make the transition toward a better legal structure in a particular country, a charter city is also valuable simply because it is an additional city. 

5. There is a severe shortage of land in the world available for conducting high-level political experiments. That is, you can buy land, but you can't easily buy the right to set up your own nation on a patch of land. To me, this seems unfortunate. The ability to create space colonies—either on space stations or asteroids—may change this in the next century or two. Expect a flowering of new political experiments. Now is the time to develop the ideas for those political experiments. 

Don't miss other John Locke posts. Links at "John Locke's State of Nature and State of War."