Between the emerging new metropolises in the third millennium, Tehran - the oldest existing city in the world- is one of the most populated and largest metropolitan areas. By 2050 Iran’s predicted population will reach to 100 million [according to World Urbanization report- UN]. Considering the fact that about 85% of this population will concentrate in the urban agglomerations, Tehran Metropolitan area, as a capital with almost more than half of the services and industries, is going to be one of the largest and most dense metropolitan regions in the World.The urban settlement in Tehran started in 6000 BC which seems to be one of the everlasting urbanization points. It has several booms in population growth and urban expansion during its history, but the most dramatic expansion was to take place after the Second World War, which gave the city the dimensions of a large metropolis. In this way, the built environment of the city was a comprehensive reflection of the stages of transition through which urban and national communities were passing. This trend amplified in 60’s by the sharp rise in crude oil price which caused lots of immigra-tions to the city and it continued after revolution and Iran-Iraq war period. According to Vanstiphout, Tehran after 70’s can be seen as a realized product of the American dream of modern town planning. When the master plan of Tehran is done by Victor Gruen (American- Austrian architect) in 1967 who was invited by the Shah of Iran, it stopped its imple-mentation by Islamic revolution but just one decade later, after the war, municipality of Tehran decided to construct most parts of the plan.

The spatial structure of a city is very complex. It is the physi¬cal outcome of the subtle interactions over centuries be-tween land markets, and topography, infrastructure, regulations, and taxation. The complexity of urban spatial struc-tures has often discouraged attempts to analyze them and even to try to relate urban policy to city shape.

Infrastructure; The catalystLoads of infrastructures which were injected to the city in a glance changed Tehran from a big city to a Megacity. It merged with cities in the north and south; Tajrish and Rey (Rhagae). Wide spread expansion of the city makes it to have exceptional spatial structure. “It has a high density combined with a mildly polycentric structure”, Bertaud said.

Land Market; The main internal economical engine of the cityIn the last decades, “for instance, a major restructuring of central government financial transfer in 1985 obliged the mu¬nicipality to look for alternative source of funds. Decision was taken to charge developers for any increase in floor

Tehran has a coast

area ratio over a maximum established by the master plan of 1991 This decision, taken to fulfill a financial objective, had more impact on the spatial structure of the city than the master plan itself.” This process was the beginning of the booming land market in the city.

Geology; The unique characteristicThe City is expanded from its ultra-dense center, the city flows upwards and outwards toward the west, oscillating between clearly planned geometry and total fractalized sprawl. There seems to have been occurred a strange kind of netting of the megacity at the foot of the Alborz mountains in an elliptically shaped mold. Actually Tehran is limited by its geological borders; the northern and eastern parts of Tehran lies higher that the southern part. There is 700 m dif-ference in altitude in the city and about 4900 m difference in the agglomeration area [highest point is Damavand peak with 5678 m and the lowest point is City of Varamin with 790 m height]. The more well-to-do districts are situated in the northern part of Tehran. Because of being situated in higher altitude they are confronted with better air condition with less smog.The southern part of the city is limited by the desert. The western side is the only open geologically corridor for future expansions. But it mostly covered by heavy industries which are the barrier between Tehran and the next city; Karaj.

“Tehran has a high potential for economic development, being the largest urban concentration between Istanbul and Mumbai. Once a public transport option has been selected, land use regulations, infrastructure investments and land taxes should be internally consistent and reinforce the option selected.” (Bertaud, 2003)

The new infrastructural projects are going to shape the Megacity of Tehran in 2050; the construction of the rest of the metro network can change the city to have a definitely polycentric structure but in the other hand, the other project; Tehran- Caspian Coast freeway, which will connect Tehran to the coast in less than an hour, will have a massive impact on the city form.

In a few years Tehran, with its floating spatial structure, will be connected to the Caspian Sea, Damavand [the ninth highest peak in the World] and the Desert [Dasht-e-Kavir] in less than an hour!The question in Does the city find its escape routes to accommodate 40 million people in 2050? Is the Caspian Sea delta region which now is working like a Leisure City for Tehran will be a part of it? Is it a process of forming new type of global city with rich environmental resources?