In the dense areas, most of the concentration is via medium- and high-rise buildings. London's skyscrapers such as 30 St Mary Axe, Tower 42, the Broadgate Tower and One Canada Square are mostly in the two financial districts, the City of London and Canary Wharf. High-rise development is restricted at certain sites if it would obstruct protected views of St Paul's Cathedral and other historic buildings. Nevertheless, there are a number of very tall skyscrapers in central London (see Tall buildings in London), including the 95-storey Shard London Bridge, the tallest building in the European Union.