<Tr> <Th_colspan="2"> Population (2017 estimate) </Th> </Tr> <Tr> <Th> Federal district </Th> <Td> 693,972 </Td> </Tr> <Tr> <Th> Rank </Th> <Td> 21st, U.S. as of 2016 incorporated places estimate </Td> </Tr> <Tr> <Th> Density </Th> <Td> 11,367 / sq mi (4,389 / km) </Td> </Tr>

Why is dc not part of a state