Rapid urbanization and urban area expansion of sub-Saharan Africa are
megatrends of the 21st century. Addressing environmental and social
problems related to these megatrends requires faster and more efficient
urban planning that is based on measured information of the expansion
patterns. Urban growth prediction models (UGPMs) provide tools for
generating such information by predicting future urban expansion
patterns and allowing testing of alternative planning scenarios. We
created an UGPM for Zanzibar City in Tanzania by measuring urban
expansion in 2004–2009 and 2009–2013, linking the expansion to
explanatory variables with a generalized additive model, measuring the
accuracy of the created model, and projecting urban growth until 2030
with the business-as-usual and various alternative planning scenarios.
Based on the results, the urban area of Zanzibar City expanded by 40%
from 2004 to 2013. Spatial patterns of expansion were largely driven by
the already existing building pattern and land-use constraints. The
created model predicted future urban expansion moderately well and had
an area under the curve value of 0.855 and a true skill statistic result
of 0.568. Based on the business-as-usual scenario, the city will expand
89% from 2013 until 2030 and will continue to sprawl to new regions at
the outskirts of the current built-up area. Establishing new urban
centers had the highest impact on directing urban expansion from the
tested alternative planning scenarios. However, the impact of all
scenarios was low and therefore also other planning solutions such as
vertical development, urban growth boundaries, and gradual improvement
of the informal areas should be considered in Zanzibar.