Secunderabad, the twin city of Hyderabad lying to its north, has a total population of 217,910 and a literacy rate of 85 percent, with Telugu and Urdu as the official languages. The city is located at an average elevation about 170 feet in the northern part of the Deccan Plateau, characterized by a hilly and rocky terrain. According to the 2011 census, the population of the entire Hyderabad District is 3.9 million and the literacy rate is 83 percent. 36 percent of the total population of the district constitutes the working age population, out of which only 4 percent are in agriculture sector, 3 percent in the household industry and the bulk 93percent in industry and services, primarily in Information Technology and Railways since Secunderabad is the Headquarter of the South Central Railway. Historically, the region was ruled by the Chalukyas, Kakatiyas and Nizams. In1798, a Treaty of Subsidiary Alliance was signed between the Nizam of Hyderabad, Sikander Jah and the British East India Company, to establish the region north of the Hussain Sagar Lake as a British cantonment named Sikandrabad / Secunderabad. By 1806, Sikandarabad was one of the most important British Cantonments, with a cosmopolitan population of British, Anglo-Indians and Parsees. Until Indias independence, the official language of the city was English and unlike Hyderabad, Secunderabad was exempted from customs duty on imported goods to make foreign trade more favorable for the Empire.