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Research Abstracts on Spatial Information ScienceCSIS DAYS 2015

Spatiotemporal analysis of urban growth in three African capital cities: A grid-cell-based analysis
Hao Hou, Ronald C. Estoque and Yuji Murayama
Graduate School of Life and Environmental Sciences, University of Tsukuba
Email: <houhao880828@gmail.com>(1) Motivation ： The purpose of this study is to
examine the spatiotemporal pattern and dynamics of
the urban growth in three African capitals ofdifferent sizes (2000-2014) using remote sensingand LandScan population data, and a grid-cell-basedmethod. Since a comparative analysis of urban landcover changes in different African capital cities
using a grid-cell-based method has not yet been
conducted, this study might be useful in the context
of urban studies and landscape and urban planningof African cities.
(2) Methodology: Maximum likelihood supervisedclassification method was employed for classifying
the Landsat imageries. Six land-cover categories
were classified, namely urban, bareland, cropland,grassland, forest and water. A grid-cell-based
method (1 km × 1 km grid cell) was used to reveal
the spatial distribution of the land-cover changes andpopulation change in density between 2000 and 2014.
The grid-cell-based analysis has three steps:
 Create 50 km × 50 km fishnet to make empty gridcells. Overlap land-cover maps with the 1 km gridcells.
 Use zonal statistics in ArcGIS® software package
to summarize the number of pixels of eachcategory contained in each grid cell.
 Combine the tables for the two time points basedon the grid cell code ID. With the combined tables,
the change in the proportion or density of eachland-cover category between the two time points
is determined.
Subsequently, the correlation between thechanges in the density of all the land-covercategories, and between the changes in the densityof the urban land-cover category and changes in
population density are determined.

(3) Data： Landsat ETM+/OLI/TIRS imageries in twotime points (2000 and 2014) were adopted to prepare
the land-cover maps (Fig.1) and detect thespatiotemporal land-cover changes in Bamako,
Cairo and Nairobi. LandScan population datasets,developed by Oak Ridge National Laboratory(ORNL), are used to determine the grid-based
population density in three cities.
(4) Results： The results show these three capital cities
have undergone a rapid urban growth in the past 14years (Fig.2a). In all three cities, a substantial loss ofbareland was detected due to urban expansion.
Bamako, classified as a small-sized African capital,
had the highest urban growth rate (7.95% per year),and this was at the expense of its bareland and green
areas (grassland and forest). On the other hand, Cairo,
classified as a big-sized African capital, had thelowest urban growth rate (3.45% per year), while
Nairobi, classified as a medium-sized African capital,
had the increase of the urban growth rate (6.97% peryear). The urban expansion of both Cairo andNairobi occurred mostly in their barelands. However,unlike Cairo, Nairobi’s green areas (especiallycropland) also decreased. The results also show thatthe spatial pattern of the changes in population
density varied across the three cities (Fig.2b). A
weak correlation between the change in urbandensity and the change in population density wasobserved in all three cities. This level of correlation
might have been affected by the vertical urban
development in the three cities, which tends toincrease population density, but has not been
captured in image analyses. Although thecorrelations were low, there was evidence for asignificant positive relationship between population
growth and urban expansion in all three cities.

Figure 1: Land-cover maps of three citiesin (a) 2000; (b) 2014

Figure 2: Density change maps of (a) urban;(b) population in three cities from 2000 to 2014

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