Connectivity and physical activity: using footpath networks to measure the walkability of built environments

There is now a strong body of research that suggests that the form of the built environment can influence levels of physical activity, leading to an increasing interest in incorporating health objectives into spatial planning and regeneration. There have been a number of strands to this research, one of which has sought to develop objective measurements of the built environment using geographic information systems involving measures of connectivity and proximity to compare the relative ‘walkability’of different neighbourhoods. The development of the ‘walkability index’ has become a popular indicator of the spatial distribution of those built environment features that are considered to have the greatest positive influence on levels of physical activity. The success of this measure is built on its ability to capture succinctly correlates of physical activity using routinely available spatial data, which includes using road centre lines to measure connectivity. In this paper we discuss two key aspects of the walkability index. First, as suggested by others, that the use of a footpath network, rather than road centre lines, may be far more effective in evaluating walkability. This may be particularly important for assessing changes in walkability arising from pedestrian-focused infrastructure projects, such as greenways. Second, we explore the implications of this for how connectivity can be measured. We take six different measures of connectivity and first analyse the relationships between them and then test their correlation with actual levels of physical activity of local residents in Belfast, Northern Ireland. We find that the best measurements appear to be intersection density and metric reach and use this finding to discuss the implications for developing tools that may better support decision-making in spatial planning.