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 1.5–9 m (5–30 ft).[61] Much of the city was originally a wetland that was reclaimed over the decades to accommodate a burgeoning population.[62] The remaining undeveloped areas, known as the East Kolkata Wetlands, were designated a "wetland of international importance" by the Ramsar Convention (1975).[63] As with most of the Indo-Gangetic Plain, the soil and water are predominantly alluvial in origin.