Since achieving independence as a result of the partition of India, the urbanisation has increased exponentially, with several different causes. The majority of the population in the south resides along the Indus River, with Karachi the most populous commercial city. In the east, west, and north, most of the population lives in an arc formed by the cities of Lahore, Faisalabad, Rawalpindi, Islamabad, Sargodha, Gujranwala, Sialkot, Gujrat, Jhelum, Sheikhupura, Nowshera, Mardan, and Peshawar. During the period 1990–2008, city dwellers made up 36% of Pakistan's population, making it the most urbanised nation in South Asia. Furthermore, more than 50% of Pakistanis live in towns of 5,000 people or more. Immigration, from both within and outside the country, is regarded as one of the main factors contributing to urbanisation in Pakistan. One analysis of the 1998 national census highlighted the significance of the partition of India in the 1940s as it relates to urban change in Pakistan.