Iran has one of the highest urban population growth rates in the world. From 1950 to 2002, the urban proportion of the population increased from 27% to 60%. The United Nations (UN) predicts that by 2030 80% of the population will live in urban areas. Most internal migrants have settled near the cities of Tehran, Isfahan, Karaj, Ahvaz, Mashhad and Qom. Tehran, with a population of 8.7 million in 2016, is the largest city in Iran and is the nation's capital. Tehran is home to around 11% of Iran's population. It is the hub of Iran's communication and transport networks.
Mashhad, with a population of 4.2 million in 2019, is the second-largest Iranian city and the centre of the province of Razavi Khorasan. Mashhad is one of the holiest Shi'a cities in the world as it is the site of the Imam Reza shrine. It is the centre of tourism in Iran. Between 15 and 20 million pilgrims go to Imam Reza's shrine every year.