Pick a city block in a great American urban neighborhood. What comes to mind?

Soho, Times Square or Park Slope in New York, perhaps? Or Chicago’s Magnificent Mile and Wicker Park? Maybe San Francisco’s North Beach, or Georgetown and Adams Morgan in D.C.?

Very different places all. But what do they have in common?

They’re great to walk along. There’s lots to do and look at, not least of all the people going about their day. The buildings on the block are tightly packed, and a variety of shops, restaurants and other spaces display any number of interesting things and activities.

Now think about South Florida. There are places like those here, too. Maybe they’re not as well known as the above, or so iconic, and maybe there are not quite so many and those we do have are scattered around.

But they’re here, and we’re asking you to find them.

The Miami Herald is holding an open competition to identify the best urban block in Miami-Dade, Broward or Palm Beach counties.

The idea: to engage South Floridians in a discussion about what makes for a rich urban texture as downtowns and urban districts, once all but left behind in the rush to the suburbs, spring back to life across the region.

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 in the manner of classic cities — through small, attached buildings that can be adapted over time to different uses.

We are soliciting photographs and short videos of your favorite urban block in the three counties, accompanied by a brief explanation of why it’s the best. Entries will be judged by five expert jurors. The winner will get a block party. Individuals will get cash prizes for best photo and video presentations.

What do we mean by a block?

Basically a street, one-block long, fronted by buildings on either side. The buildings could also front a plaza, a small park or square, or a pedestrian-only passageway. There should be ample sidewalks, good buildings and a mix of shops, homes and activities to draw people to it. It can be old, or new, or a smooth blend of both.

We’re looking in particular for that hard-to-define combination of housing, commerce, work, transportation, street life and architecture that makes a block a great South Floridaplace, one to come back to time and again, and one to emulate as our towns and cities seek to rebuild their urban neighborhoods.

“A great block is a microcosm of a great city,’’ said Howard Davis, a professor of architecture at the University of Oregon and author of Living Over the Store, a definitive history of buildings that mix living and working, which many urbanists believe to be the basic building blocks of cities.

Here’s what Davis said when The Herald and The Townhouse Center’s Andrew Frey asked him to outline key elements of an ideal great block:

“I would encourage people to look for people. A single block, to me, is potentially big enough and diverse enough so that you’ve got a real variety of people, old and young, rich and poor, and there is a real diversity of uses. I would want to see that diversity of a city’s population reflected on the block,’’ he said.