A spatially-explicit sensitivity analysis of urban definitions: Uncovering implicit assumptions in the Degree of Urbanisation

We introduce a spatially-explicit sensitivity framework to uncover potential biases in urban delineation approaches. Our starting point is that there is no broadly shared agreement on how to define or delineate urban areas, neither in terms of methods nor in terms of thresholds or criteria. Deciding on delineation criteria thus inevitably involves making certain assumptions that may unwittingly reproduce urban realities experienced by those expressing them, and have spatially unequally distributed implications. Understanding how specific criterion choices shape our understanding of 'the urban' and how, why, and - especially - where a definition leads to specific sensitivities is therefore key, especially when the definition is utilised beyond its intended application. Our framework to uncover these sensitivities is spatially explicit in the sense that it does not rely on aggregate statistics but instead focuses on the sensitivity of the 'urban' classification of individual spatial units at the finest spatial granularity. Applying the framework to the definition of the Degree of Urbanisation reveals that sensitivity is indeed not equally distributed across the world. Certain regions (e.g., areas around Dallas - Fort Worth) and specific types of urbanisation (e.g., desakota regions in Pacific Asia) exhibit higher sensitivity than others. We discuss how these sensitivities may embody certain implicit assumptions in the definition, and examine their broader theoretical implications.