The Northern line is a London Underground line which runs between North London and South London. It is printed in black on the Tube map. It carries more passengers per year than any other Underground line – around 340 million in 2019 – making it the busiest tube line in London. The Northern line is unique on the network in having two routes through Central London, two northern branches and two southern branches. Despite its name, it does not serve the northernmost stations on the Underground, though it does serve the southernmost station at Morden, the terminus of one of the two southern branches.