1 Geographic Data Science Lab, Department of Geography and Planning, University of Liverpool, Liverpool L69 7ZT, UK; MRC/CSO Social and Public Health Sciences Unit, University of Glasgow, Glasgow, UK. Electronic address: mark.green@liverpool.ac.uk.
2 Department of Health Services Research and Policy, London School of Hygiene and Tropical Medicine, London, UK.
3 MRC/CSO Social and Public Health Sciences Unit, University of Glasgow, Glasgow, UK.