We used to know how to do this in America — how to build a convivial, walkable, prosperous city neighborhood of shops, workplaces and homes that drew people to it like the proverbial bee to honey.

Then came the car, and out went everything we knew. Life and commerce drained out of cities and downtowns as people followed the lure of far-flung suburbs made possible only by the automobile.

Out there, zoning laws banned the traditional city block, the cheek-by-jowl mix of people and activities that gave rise to civilization thousands of years ago. Single-use zoning mandated the strict division of home, workplace and commercial place, each separated from the other by gulfs of highways and automobile arterials that made trying to walk anywhere a fool’s errand, not to mention dangerous.

For the longest time, Americans who wanted to experience the pedestrian-friendly charms and dynamism of a “real city’’ had to fly to Paris or Rome or Barcelona, old places the automobile colonized but never conquered entirely.

Now we’re taking another look at this arrangement.

From Pittsburgh to Denver to New York, from West Palm Beach to Tampa to Miami, young people, families and retirees who have tired of the ‘burbs and their endless traffic congestion are flocking back to once-dormant, even blighted downtowns and urban neighborhoods, reigniting urban economies. New U.S. Census Bureau figures show that big U.S. cities are growing in population.

In recognition of this consequential trend, The Miami Herald is launching an open competition to identify the best urban block in South Florida. The Herald is sponsoring the contest in conjunction with WLRN/Miami Herald News, El Nuevo Herald, the John S. and James L. Knight Foundation and the Townhouse Center, a new Miami non-profit that promotes the development of urban neighborhoods through small, attached buildings that can be adapted over time to different uses.

Why are we doing it?

As towns and cities seek to retool their downtowns and urban districts to lure new businesses and residents, the time seems ripe for a refresher on what makes a good city block — what it might look like, what the key ingredients are, how it ought to function and feel. That refresher is especially needed now because over the years suburban-style development and zoning invaded, and sometimes sped the devastation of, our urban cores.

We’re talking about strip malls with parking lots fronting streets redesigned as highways, impractically narrow sidewalks, yawning parking garage bays on main streets, and lots of blank walls — stuff that doesn’t make good urban places.

Giving exposure to great blocks can also provide a proven model as sprawling suburban communities increasingly try to retrofit to create the pedestrian-oriented urban centers they never had.

And what better place to look for examples than right at home? Although South Florida development took off with the car and the air conditioner, and the region has become synonymous with suburban sprawl, its main cities and original suburbs predate that, and their cores were designed on a traditional, dense city grid.

That means that wonderful, walkable, steeped-in-South-Florida blocks abound if you know where to go. Some have recently found new life. Others never faded. We don’t want to exert undue influence by pointing them out. But many are hardly a secret.