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Abstract
In light of rapid global urbanisation, monitoring and mapping of urban and population growth is of great importance. Population growth in Sana’a was investigated for this reason. The capital of the Republic of Yemen is a rapidly growing middle sized city where the population doubles almost every ten years. Satellite data from four different sensors were used to explore urban growth in Sana’a between 1989 and 2007, assisted by topographic maps and cadastral vector data. The analysis was conducted by delineating the built-up areas from the various optical satellite data, applying a fuzzy-rule-based composition of anisotropic textural measures and interactive thresholding. The resulting datasets were used to analyse urban growth and changes in built-up density per district, qualitatively as well as quantitatively, using a geographic information system. The built-up area increased by 87 % between 1989 and 2007. Built-up density has increased in all areas, but particularly in the northern and southern suburban districts, also reflecting the natural barrier of surrounding mountain ranges. Based on long-term population figures, geometric population growth was assumed. This hypothesis was used together with census data for 1994 and 2004 to estimate population figures for 1989 and 2007, resulting in overall growth of about 240%. By joining population figures to district boundaries, the spatial patterns of population distribution and growth were examined. Further, urban built-up growth and population changes over time were brought into relation in order to investigate changes in population density per built-up area. Population densities increased in all districts, with the greatest density change in the peripheral areas towards the North. The results reflect the pressure on the city’s infrastructure and natural resources and could contribute to sustainable urban planning in the city of Sana’a.
Highlights
Urbanisation is a worldwide trend in the 21st century
The United Nations Population Division (UNPD) estimates that most population growth in the 30 years will occur in urban agglomerations
In order to account for sealed areas around the buildings and the off-nadir acquisition angle of the Quickbird data leading to slightly larger building areas than the digitized building footprints from a near-nadir view, the dataset was buffered by 5 m
Summary
Urbanisation is a worldwide trend in the 21st century. The United Nations Population Division (UNPD) estimates that most population growth in the 30 years will occur in urban agglomerations. Already today approximately 50 % of the human population is living in urban areas. While the most rapid growth is predicted for cities in less developed countries, it is expected that small and middle sized urban areas will absorb most of this growth [1]. Yemen is a southwest Asian country characterised by rapid urbanisation.
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