Situated in the northern center of the country, Tehran is Iran’s capital city – which is also its largest city. Iran is situated between the Middle East and Asia and has a history of changing its capital city – Tehran being the 32nd one chosen. The population of the city of Tehran has been steadily growing over the last few decades and is now around 8.3 million. There is an estimated number of nearly 8.5 million in the middle of 2014. Interestingly, the Tehran metro system, which opened in 1999 - currently boasts the cleanest train carriages in the world.