"A good city is like a good party--you stay for longer than you plan," says Danish architect Jan Gehl. He believes that good architecture is not about form, but about the interaction between form and life. Over the last 50 years, Gehl has changed the way that we think about architecture and city planning--moving from the Modernist separation of uses to a human-scale approach inviting people to use their cities.

At a time when growing numbers are populating cities, planning urban spaces to be humane, safe, and open to all is ever-more critical. With the help of Jan Gehl, we can all become...