Mapping the Slums of Dhaka from 2006 to 2010

Background. Rapid urban growth in low and middle income countries is frequently characterized by informal developments. The resulting social segregation and slums show disparities in health outcomes for the populations of the world’s megacities. To address these challenges, information on the spatial distribution of slums is necessary, yet the data are rarely available. The goal of this study was to use a remote sensing based approach to map urban slums in Dhaka, the second fastest growing megacity in the world. Methods. Slums were mapped through the visual interpretation of Quickbird satellite imagery between the years 2006 and 2010. Ancillary references included the 2005 census and mapping of slums, Google Earth, and geolocated photographs. The 2006 slums were first delineated and filtered in GIS to avoid small, isolated slums. For 2010, changes to the 2006 slums were defined over the latter’s polygons to retain border consistency. Conclusions. The dataset presented here can be considered a stepping stone for further research on slums and urban expansion in Dhaka. The slum distribution dataset is useful to be pooled with other data to reveal trends of informal settlement growth for local health policy advice in Dhaka. 1. Introduction Within recent decades, high rates of urbanization in low and middle income countries led to the development of megacities with more than 10 million inhabitants [1, 2]. Megacity development is often combined with a loss of governability due to weak political structures [2]. In addition, health and social infrastructures are poor or nonexistent, and the housing sector is incapable of fulfilling the demand of the high numbers of rural migrants flushing into the cities every day [3]. In Dhaka, the capital city of Bangladesh, the population increases by half a million each year, a rate that would result in a population of almost 23 million by 2025 [1, 4]. With over 15 million inhabitants today, Dhaka is the second fastest growing megacity in the world [1]. Many of the city’s immigrants initially concentrate in slums, due to poverty and limited alternatives [5]. Within the slums, poor environmental conditions and deprived infrastructures can be found [4, 6, 7]. These induce negative impacts on the physical and psychological well-being of urban slum residents [8–12]. The Centre for Urban Studies estimated that the total population of Dhaka’s slums was more than doubled between 1996 and 2005, from 1.5 to 3.4 million people. The limited knowledge about slum settlement size, distribution, and dynamics presents an enormous challenge