Today Venice is recognized as part of the artistic and architectural patrimony of all humanity, a fitting role for a city whose thousand-year economic and political independence was sustained by its role in global trading. The situation of the city on islands has limited modern suburban spread beyond the historic centre; its framework of canals and narrow streets has prevented the intrusion of automobiles; and its unmatched wealth of fine buildings and monuments dating from the period of commercial dominance has ensured a keen and almost universal desire for sensitive conservation. This concern for conservation is now extended not just to the city’s monuments but to the very city itself, as rising water levels and subsidence of the land upon which Venice is built threaten the continued existence of the city in its present form. In 1987 Venice and its lagoon were collectively designated a UNESCO World Heritage site. Pop. (2009 est.) city, 59,984; (2011 est.) comune, 270,884.