Figures here are for the Office for National Statistics defined Outer London (in its 2001 limits), whose land area is 1,254 km2 (484 sq. miles). Figures before 1971 have been reconstructed by the Office for National Statistics based on past censuses in order to fit the 2001 limits. Figures from 1981 onward are midyear estimates, with those for 2002 to 2009 having been revised during 2010. These mid-year estimates are more accurate than the censuses themselves, which are known to underestimate the population of London.