Trinamool Congress. The city's economic recovery gathered momentum after the 1990s, when India began to institute pro-market reforms. Since 2000, the information technology (IT) services sector has revitalised Kolkata's stagnant economy. The city is also experiencing marked growth in its manufacturing base. Geography Spread roughly north–south along the east bank of the Hooghly River, Kolkata sits within the lower Ganges Delta of eastern India approximately 75 km (47 mi) west of the international border with Bangladesh; the city's elevation is . Much of the city was originally a wetland that was reclaimed over the decades to accommodate a burgeoning population. The remaining undeveloped areas, known as the East Kolkata Wetlands, were designated a "wetland of international importance" by the Ramsar Convention (1975). As with most of the Indo-Gangetic Plain, the soil and water are predominantly alluvial in origin. Kolkata is located over the "Bengal basin", a pericratonic tertiary basin. Bengal basin comprises three structural units: shelf or platform in the west; central hinge or shelf/slope break; and deep basinal part in the east and southeast. Kolkata is located atop the western part of the hinge zone which is about wide at a depth of about below the surface. The shelf and hinge zones have many faults, among them some are active. Total thickness of sediment below Kolkata is nearly above the crystalline basement; of these the top is Quaternary, followed by of Tertiary sediments, trap wash of Cretaceous trap and Permian-Carboniferous Gondwana rocks. The quaternary sediments consist of clay, silt and several grades of sand and gravel. These sediments are sandwiched between two clay beds: the lower one at a depth of ; the upper one in thickness. According to the Bureau of Indian Standards, on a scale ranging from in order of increasing susceptibility to earthquakes, the city lies inside seismic zone III. Urban structure The Kolkata metropolitan area is spread over and comprises 4 municipal corporations (including Kolkata Municipal Corporation), 37 local municipalities and 24 panchayat samitis, as of 2011. The urban agglomeration encompassed 72 cities and 527 towns and villages, as of 2006. Suburban areas in the Kolkata metropolitan area incorporate parts of the following districts: North 24 Parganas, South 24 Parganas, Howrah, Hooghly and Nadia. Kolkata, which is under the jurisdiction of the Kolkata Municipal Corporation (KMC), has an area of . The east–west dimension of the city is comparatively narrow, stretching from the Hooghly River