From the Wikipedia page 
North Greenwich is a 19th century name for the southern tip of the Isle of Dogs, located in the London Borough of Tower Hamlets. It was named for the now defunct North Greenwich Railway Station (1872), that served a former passenger ferry to Greenwich and stood near the later Island Gardens (1897) and Greenwich foot tunnel (1902). It faces Greenwich over the River Thames and the area is now more usually known as South Millwall.
It should not be confused with the northern part of the Greenwich peninsula in South London, formerly known as East Greenwich that lies south of the river and is the site of the The O2 (formerly the Millennium Dome). The opening in 1999 of the North Greenwich Station on London Underground's Jubilee Line has now led to this area being known colloquially as North Greenwich.