ChartCumulative number of sitesCumulative area (square km)18381899190519101913191619191922192519281931193419371940194319461949195219551958196119641967197019731976197919821985198819911994199720002003200620092012201501000020000300004000050000600007000080000900001000001100001200000250000500000750000100000012500001500000Number of sitesSquare km