Added on April 10, 2014: Reasons Why They Are Concrete Pavements
The sizes and textures of individual squares are similar. They are about 30 meters by 40 meters and show few variations on the surface. There are no diagonal lines or curving lines. Nature could not form such geometry. Farm plots are rarely so regular in size and shape. If it were a farmland, farmers would not have divided it into a thousand plots, each as small as 1,200 square meters.Moreover, farm plots could not have kept those boundaries of the squares after Martian farmers had died out three billion years ago.On the other hand, numerous concrete pavements have been found on Mars: http://wretchfossil.blogspot.tw/2013/07/curiosity-found-advanced-martians.html
Added on April 11: White Calcium Seeping out of Concrete? In the “Squares of Mars”, there are some depressions. In the depressions there is white material such as this:https://www.flickr.com/photos/fossil_lin/13813702593/
The white material does not look like the soil of farm plots. It looks more like calcium, which may have seeped out of the concrete pavements.
Added on April 12: Reasons Why They Are Not Stone Pavements or Tiles
The whole area is over 5 million square meters. On the bottom and higher ground, there are irregularly shaped puzzle pieces. Some of the pieces measure over 5,000 square meters. So, they are not stone pavements or tiles.