I was asked to give an urban planner’s perspective on the article in this issue of the journal by Li et al.¹ What is most striking about this article is the fact it was written at all. It represents the engagement of two fields (heading toward marriage) that were hardly aware of each other 10 years ago, and barely speaking five years ago.

For about 20 years, the urban and transportation planning fields have been researching the relation between the built environment and travel choices, including the choice to walk or cycle.^2–4 The built environment has been measured in objective terms, using gross measures such as population density, land use mix, and street connectivity. In recent years, measurements have relied heavily on geographical information system (GIS) technology. The behaviour of …