This article is about the demographic features of the population of Saudi Arabia, including population density, ethnicity, education level, health of the populace, economic status, religious affiliations and other aspects of the population. Saudi Arabia’s population as of the April 2010 Census was 27,136,977: 18,707,576 Saudi nationals and 8,429,401 non-nationals. About 51% of the population is under the age of 25 (as of Feb 2012). Until the 1960s, most of the population was nomadic or seminomadic; due to rapid economic and urban growth, more than 95% of the population now is settled. 80% of Saudis live in three major urban centers—Riyadh, Jeddah, or Dammam. Some cities and oases have densities of more than 1,000 people per square kilometer (2,600/mile²). Saudi Arabia’s population is characterized by rapid growth and a large cohort of youths. Saudi Arabia hosts one of the pillars of Islam, which obliges all Muslims to make the Hajj, or pilgrimage to Mecca, at least once during their lifetime if they are able to do so. The cultural environment in Saudi Arabia is highly conservative; the country adheres to a strict interpretation of Islamic religious law (Shari’a). Cultural presentations must conform to narrowly defined standards of ethics. Men and women are not permitted to attend public events together and are segregated in the work place. Most Saudis are ethnically Arab of whom they immigrated as pilgrims and reside in the Hijaz region along the Red Sea coast such as Jeddah, Mecca and Medina. According to a random survey, most would-be Saudis come from the Subcontinent and Arab countries. Many Arabs from nearby countries are employed in the kingdom. There also are significant numbers of Asian expatriates mostly from India, Pakistan, Bangladesh, Indonesia and the Philippines. In the 1970s and 1980s, there was also a significant community of South Korean migrant labourers, numbering in the hundreds of thousands, but most have since returned home; the South Korean government’s statistics showed only 1,200 of their nationals living in the kingdom . There are more than 100,000 Westerners in Saudi Arabia, most of whom live in private compounds in the major cities such as Riyadh, Jeddah and Dhahran. The government prohibits non-Muslims from entering the cities of Mecca and Medinah.