How do we accommodate a growing urban population in a way that is sustainable, equitable, and inviting? This question is becoming increasingly urgent to answer as we face diminishing fossil-fuel resources and the effects of a changing climate while global cities continue to compete to be the most vibrant centers of culture, knowledge, and finance.

Jan Gehl has been examining this question since the 1960s, when few urban designers or planners were thinking about designing cities for people. But given the unpredictable, complex and ephemeral nature of life in cities, how can we best design...