Improving the measurement of urban sprawl: Weighted Urban Proliferation (WUP) and its application to Switzerland

Growing urban sprawl is a serious concern worldwide for a number of environmental and economic reasons and is a major challenge on the way to sustainable land use. To address this increasing problem, there is an urgent need for quantitative measurement. Every meaningful method to measure the degree of urban sprawl needs to be based on a clear definition of urban sprawl disentangling causes and consequences of urban sprawl from the phenomenon of urban sprawl itself, as urban sprawl has differing causes and consequences in different regions and regulatory contexts. Weighted Urban Proliferation (WUP) ― the novel method presented in this paper ― is based on the following definition of urban sprawl: the more area built over in a given landscape (amount of built-up area) and the more dispersed this built-up area in the landscape (spatial configuration), and the higher the uptake of built-up area per inhabitant or job (lower utilization intensity in the built-up area), the higher the degree of urban sprawl. However, there is a lack of reliable measures of urban sprawl that integrate these three dimensions in a single metric. Therefore, these three independent dimensions need to be combined according to the qualitative assessment of sprawl to create a suitable metric ― which is exactly what the WUP metric does using two weighting functions. Switzerland serves as an example of applying this method to examine the current state, for comparisons among regions, for historical analysis, and for assessing planning scenarios. The degree of urban sprawl in Switzerland increased by 155% between 1935 and 2002, and without rigorous measures, scenarios of future urban sprawl show that it is likely to further increase by more than 50% until 2050. Examples from parts of Switzerland demonstrate that sprawl can be reduced. As a consequence of intense public discussion, the Swiss Spatial Planning Act was revised in 2013 to make it tighter. We conclude that the new method is more suitable than previous methods to quantify the indicator urban sprawl in monitoring systems, e.g., it has now been implemented in monitoring systems in Switzerland. The new WUP method is highly suitable for performance control of limits to urban sprawl once they are implemented and for application to other countries around the globe.