Portsea Island

Portsea Island is a flat, low-lying island 24.5 square kilometres in area, just off the southern coast of England in the county of Hampshire, which contains the majority of the city of Portsmouth.

Portsea Island has the third-largest population of all the islands in the British Isles after the mainlands of Great Britain and Ireland; it also has the highest population density of any British Isle, and Portsmouth has the highest population density of any city in the UK outside of London.To the east of Portsea Island lies Hayling Island, separated by Langstone Harbour. To the west is the peninsular mainland town of Gosport, separated by Portsmouth Harbour.