The United Arab Emirates is situated in the Middle East and southwest Asia, bordering the Gulf of Oman and the Persian Gulf, between Oman and Saudi Arabia; it is at a strategic location along the northern approaches to the Strait of Hormuz, a vital transit point for world crude oil. The UAE lies between 22°50′ and 26° north latitude and between 51° and 56°25′ east longitude. It shares a border with Qatar on the northwest, a border with Saudi Arabia on the west, south, and southeast, and a border with Oman on the southeast and northeast. The land border with Qatar in the Khawr al Udayd area is a source of long-running dispute (in fact, whether it even shares a land border with Qatar is in dispute). The total area of the UAE is approximately . The country's exact size is unknown because of disputed claims to several islands in the Persian Gulf, because of the lack of precise information on the size of many of these islands, and because most of its land boundaries, especially with Saudi Arabia, remain undemarcated. The largest emirate, Abu Dhabi, accounts for 87 percent of the UAE's total area (). The smallest emirate, Ajman, encompasses only . Boundaries The UAE stretches for more than along the southern shore of the Persian Gulf. Most of the coast consists of salt pans that extend far inland. A recent global remote sensing analysis suggested that there were 637km² of tidal flats in the United Arab Emirates, making it the 40th ranked country in terms of tidal flat extent. The largest natural harbor is at Dubai, although other ports have been dredged at Abu Dhabi, Sharjah, and elsewhere. Numerous islands are found in the Persian Gulf, and the ownership of some of them has been the subject of international disputes with both Iran and Qatar. The smaller islands, as well as many coral reefs and shifting sandbars, are a menace to navigation. Strong tides and occasional windstorms further complicate ship movements near the shore. These northern emirates on the Persian Gulf and Gulf of Oman are part of the Gulf of Oman desert and semi-desert ecoregion. South and west of Abu Dhabi, vast, rolling sand dunes merge into the Rub' al Khali (Empty Quarter) of Saudi Arabia. The desert area of Abu Dhabi includes two important oases with adequate underground water for permanent settlements and cultivation. The extensive