In the first of our series looking at the data behind individual cities, we examine the Iranian capital and find a loud, smokey metropolis that's exciting investors.
To the outside world, Iran has been overtaken by images of its leaders on podiums. As a city, Tehran has become synonymous with the political language of those men. If you want to get past the hyperbole, data speaks volumes.
Five rail lines
In 1999, line 5, the first of the Tehran metro system was opened to the public. Since then, it's been joined by four others (lines 1, 2, 3 and 4) and the carriages that travel along its air conditioned tunnels are considered the cleanest in the world.