The planning system has three tiers - national, provincial and local (city and county), and three categories - general, special and regional. But, in practice, there can be more than three tiers. For instance, governments of townships and development zones sometimes make their own special or regional plans, with the Yangtze River Delta plan encompassing three provincial-level regional plans. While work continues on the general plans at the three levels of government, special and regional plans, involving such things as urban development, environmental protection and industrial development are also worked on. The People's Liberation Army also has to make a general plan, and requires its navy, air force, missile force and armaments and logistics departments to submit separate plans. Giant state conglomerates such as China's Aerospace Science and Industry Group, which designs and manufactures missile and satellite launch systems, also have to submit their five-year plans. Economist Dr Yi Xianrong , from the Chinese Academy of Social Sciences, says there are more than 10,000 such plans, with at least 100,000 supporting documents.