Portsea Island is a small, flat and low lying island

Island

An island or isle is any piece of sub-continental land that is surrounded by water. Very small islands such as emergent land features on atolls can be called islets, cays or keys. An island in a river or lake may be called an eyot , or holm...

 just off the south coast of England

England

England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

. The island is totally within, and contains a large proportion of, the city of Portsmouth

Portsmouth

Portsmouth is the second largest city in the ceremonial county of Hampshire on the south coast of England. Portsmouth is notable for being the United Kingdom's only island city; it is located mainly on Portsea Island...

. It has the third-largest population of any island in the British Isles

British Isles

The British Isles are a group of islands off the northwest coast of continental Europe that include the islands of Great Britain and Ireland and over six thousand smaller isles. There are two sovereign states located on the islands: the United Kingdom of Great Britain and Northern Ireland and...

, after the mainlands of Great Britain

Great Britain

Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...

 and Ireland

Ireland

Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...

.
To the east lies Langstone Harbour

Langstone Harbour

Langstone Harbour is an inlet of the English Channel in Hampshire, sandwiched between Portsea Island to the south and west, Hayling Island to the south and east, and Langstone to the north. Geographically it is a ria....

, and to the west is Portsmouth Harbour

Portsmouth Harbour

Portsmouth Harbour is a large natural harbour in Hampshire, England. Geographically it is a ria: formerly it was the valley of a stream flowing from Portsdown into the Solent River. The city of Portsmouth lies to the east on Portsea Island, and Gosport to the west on the mainland...

. To the south it faces into the Solent

Solent

The Solent is a strait separating the Isle of Wight from the mainland of England.The Solent is a major shipping route for passengers, freight and military vessels. It is an important recreational area for water sports, particularly yachting, hosting the Cowes Week sailing event annually...

. A small channel, known as Portsbridge Creek

Portsbridge Creek

Portsbridge Creek is a tidal waterway that runs between Portsea Island and the mainland from Langstone Harbour to Tipner Lake...

, separates the island from the mainland, Great Britain

Great Britain

Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...

.

Three road bridges (the M275 motorway

M275 motorway

The M275 is a long, dual three-lane motorway in the county of Hampshire, southern England. It is the principal route for entering and leaving Portsmouth. It continues as the A3 into Portsmouth, and meets the M27 at its northern terminus...

, the A3

A3 road

The A3, known as the Portsmouth Road for much of its length, is a dual carriageway, or expressway, which follows the historic route between London and Portsmouth passing close to Kingston upon Thames, Guildford, Haslemere and Petersfield. For much of its length, it is classified as a trunk road...

 and the A2030

A2030 road

The A2030 is a road in Hampshire. The road starts off at junction 5 of the A3, near the village of Bedhampton. The road then runs west along the base of Portsdown Hill, following the old route of the A27 into Portsmouth until it reaches the Drayton area...

), a pedestrian and cycle bridge, and a rail bridge connect the island to the mainland, and a small road bridge joins it to Whale Island. In addition there are ferry services to Gosport

Gosport

Gosport is a town, district and borough situated on the south coast of England, within the county of Hampshire. It has approximately 80,000 permanent residents with a further 5,000-10,000 during the summer months...

 (on the mainland), Hayling Island

Hayling Island

-Leisure activities:Although largely residential, Hayling is also a holiday, windsurfing and sailing centre, the site where windsurfing was invented....

 and the Isle of Wight

Isle of Wight

The Isle of Wight is a county and the largest island of England, located in the English Channel, on average about 2–4 miles off the south coast of the county of Hampshire, separated from the mainland by a strait called the Solent...

.

There have been two Bronze Age hoards found on the island. A hoard of Roman coins has also been found.

The name of Portsea

Portsea

Portsea is an area of the English city of Portsmouth, located on Portsea Island, within the ceremonial county of Hampshire.The area was originally known as the Common and lay between the town of Portsmouth and the nearby Dockyard. The Common started to be developed at the end of the seventeenth...

is also used for an administrative district of Portsmouth, located in the south-west corner of the island.