The Victoria Line is part of the London Underground system and is a deep-level line running from the south-west to the north-east of London. It is coloured light blue on the Tube map and is the busiest line on the network, in terms of how many passengers it carries per annum. It is the only line on the Underground, except for the two-stop Waterloo & City Line, where the entire line is operated underground, with the only section of track to emerge above ground being the route to the depot from Seven Sisters to Northumberland Park.