Ming China's sources of salt were widespread: 80% of the salt produced, however, came from the seacoast. There were five sources of salt: seawater, salt lakes, brine wells, saline rock, and salty earth. Boiling and solar evaporation were the major production methods. The simplicity of the boiling method favored its wide use. The industry was characterized by state control through, successively five different systems: the kaizhong system, the yin system, the gang system, and the hukou shiyan system. Salt was usually shipped along natural trade routes. As a quasi-government business, administration of the salt trade was influenced greatly by the structure of civil administration, and salt distribution paralleled closely the administrative hierarchy.