sentences:  Since then, however, mayoral and non-mayoral combined authorities have been created that serve as means of strategic governance in all six metropolitan counties, with various powers allocated depending on the devolution deals negotiated between the borough councils and central government.The metropolitan counties have population densities of between 900 (South Yorkshire) and 3,200 (West Midlands) people/km².Individual metropolitan districts range from 4,000 people/km² in Liverpool to only 500 people/km² in Doncaster.