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(Reuters) - Here is a look at London's underground network, which is the biggest and the oldest in the world and turned 150 years old on Wednesday:
* The London Underground system has 275 stations.
* The Metropolitan, or Met - opened on January 9, 1863 and the first stretch measured nearly four miles and ran between Paddington (Bishop's Road) and Farringdon Street.
* The Tube is one of the world's deepest metro systems. Its deepest point is under Hampstead Heath in north London where it descends to 67 meters (220 feet). The Piccadilly Line, hit by one of the July 7, 2005 blasts is among the deepest on the network, which hampered rescue efforts.
* The Tube network has 253 miles of track and consists of 12 lines. At 34 miles, the east-west Central Line is the longest. The Jubilee line was the last to open in 1979 and that was extended through services from Stanmore to Stratford in 1999.
* Less than half of the network is actually underground. As the track heads out to London's sprawling suburbs it emerges to run largely above ground. More than 3 million passengers use the Tube each day. Passenger numbers exceeded 1.1 billion for the first time during the 2010/11 financial year.
Sources: Reuters/Transport for London
Reporting by David Cutler, London Editorial Reference Unit