CONCEPTShttp://cat.aii.caas.cn/concept/30582cat.aii.caas.cnhttp://stitch.cs.vu.nl/vocabularies/rameau/ark:/12148/cb119313712stitch.cs.vu.nlhttp://www.fao.org/countryprofiles/geoinfo/geopolitical/resource/United_States_of_Americawww.fao.org。