Greater London encompasses a total area of 1,583 square kilometres (611 sq mi), an area which had a population of 7,172,036 in 2001 and a population density of 4,542 inhabitants per square kilometre (11,760/sq mi). The extended area known as the London Metropolitan Region or the London Metropolitan Agglomeration, comprises a total area of 8,382 square kilometres (3,236 sq mi) has a population of 13,709,000 and a population density of 1,510 inhabitants per square kilometre (3,900/sq mi). Modern London stands on the Thames, its primary geographical feature, a navigable river which crosses the city from the south-west to the east. The Thames Valley is a floodplain surrounded by gently rolling hills including Parliament Hill, Addington Hills, and Primrose Hill. The Thames was once a much broader, shallower river with extensive marshlands; at high tide, its shores reached five times their present width.
What was the population density of Greater London in 2001? (If the question is unanswerable, say "unanswerable")
4,542 inhabitants per square kilometre (11,760/sq mi)