What are the Provinces of Iran?

Iran is divided into 31 provinces (ostans), each headed by a governor-general appointed by the national government and divided into counties (shahrestans). Iran has had provinces for thousands of years, from the satrapies of the ancient Persian Empire, but the modern system dates from 1937, when the country was reorganised into numbered ostans. Many of these were later renamed after historic regions or their capitals, and the larger provinces were split as the population grew. Khorasan, once Iran's largest province, was divided into three in 2004, and Alborz was separated from Tehran Province in 2010. The provinces vary hugely in size, from tiny Alborz to the deserts of Kerman and Sistan and Baluchestan.