Year	sq. km
1961	499780
1962	499780
1963	499780
1964	499780
1965	499780
1966	499780
1967	499780
1968	499780
1969	499780
1970	499780
1971	499780
1972	499780
1973	499780
1974	499750
1975	499630
1976	499570
1977	499540
1978	499530
1979	499540
1980	499470
1981	499460
1982	499460
1983	499430
1984	499440
1985	499440
1986	499440
1987	499440
1988	499440
1989	499440
1990	499440
1991	499440
1992	499440
1993	499440
1994	499440
1995	499440
1996	499440
1997	499440
1998	499440
1999	499440
2000	499000
2001	498520
2002	499040
2003	499210
2004	499180
2005	499090
2006	498980
2007	499110
2008	498800
2009	498660
2010	500010
2011	499880
2012	500210
2013	500210
2014	500210
2015	499661
2016	499564
2017	499547.35
2018	499603.479
2019	499570.036
2020	499556.645
2021	499733.244