The Sultanate of Yogyakarta which during the struggle for Independence and subsequently has been known as the Special Region of Yogyakarta, is located in the southern part of Central Java. It constitutes much of the heartland of Javanese culture, for Yogyakarta was the centre of the pre-colonial Kingdom of Mataram. Within Yogyakarta, there is a marked contrast in the population density between Bantul and Sleman regencies on one hand, and Gunung Kidul and Kulon Progo on the other hand. The basic reason for this difference is the fact that the soil of Bantu and Sleman is primarily young and volcanic, there are also a good water supply and irrigation network. The annual rate of population growth in Yogyakarta is much lower compared to other provinces in Java. This region experienced a net loss of population through migration and that the losses were greater in the poorer areas of Gunung Kidul and Kulon Progo.