Where are the deserts?

About 1/7 of the world's land is occupied with hot deserts. Many of the deserts are just a piece of barren land full of sand, others have many kinds of plants and animals living there. The deserts are placed along the lines of the Tropics, around the latitudes of 30'N and 30'S, forming parellel bands on each side of the Equator. As we can see, almost all of the deserts are located in the middle of continents and are really large pieces of land.