File:Part of Oahu as seen from a helicopter.jpg
Helicopter view of Oahu – Image credit : wikipedia

Oahu known as “The Gathering Place” is the third-largest of the Hawaiian Islands. It is home to about two-thirds of the population of the U.S. state of Hawai‘i. The state capital, Honolulu, is on O‘ahu’s southeast coast. Including small associated islands such as Ford Island and the islands in Kāne‘ohe Bay and off the eastern (windward) coast, its area is 596.7 square miles (1,545.4 km2), making it the 20th-largest island in the United States.

O‘ahu is 44 miles (71 km) long and 30 miles (48 km) across. Its shoreline is 227 miles (365 km) long. The island is composed of two separate shield volcanoes: the Wai‘anae and Ko‘olau Ranges, with a broad “valley” or saddle (the central O‘ahu Plain) between them. The highest point is Ka‘ala in the Wai‘anae Range, rising to 4,003 feet (1,220 m) above sea level
Source : wikipedia