Tehran is the capital of Iran and Tehran Province. Tehran is Iran's largest city, and the largest city in Western Asia. Tehran is ranked 29th in the world by the population of its metropolitan area. Tehran features a semi-arid, continental climate. Tehran's climate is largely defined by its geographic location, with the towering Alborz Mountains to its north and the central desert to the south. It can be generally described as mild in the spring and autumn, hot and dry in the summer, and cold in the winter. Because the city is large with significant differences in elevation among various districts, the weather is often cooler in the hilly north than in the flat southern part of Tehran.