In November 2011, it was noticed that China has been making large things in the Gobi desert, near the border with Mongolia. The structures and patterns are quite visible to sattelites and have no apparent function. The most ridiculous explanation I have heard is that they are designed as targets for spy satellites to focus on. The US and Russia have spy satellites and no one has noticed either of those countries building such things. The United States does have aerial photo calibration targets which are used to test the resolution of airborne cameras. They were designed to help spyplanes that flew at altitudes of around 80,000 feet, and now are used to calibrate the drones’ cameras. They are much much smaller than the things the Chinese are building.
Look at the following photos. On the left in each is a Gobi desert structure. On the right is a part of the lines on the Nazca Plain.