There are no guarantees when it comes to public spaces. A treasured park or favorite street can succumb to unexpected assaults--the sudden appearance of a big development project that will forever deface the neighborhood, for instance, or the gradual nibbling by the auto that eventually adds up to a huge bite being taken out of the place.

Creating a great place does not end once the trees are planted or the paths paved.

The places profiled here are in varying stages of transition from greatness to something less. Yet, thankfully, all of these places show the potential to overcome the obstacles now before them and become truly great once again. Each of them also offers a cautionary tale reminding us that creating a great place does not end once the trees are planted or the pedestrian paths paved. It is a process that evolves over time and demands constant attention. As we at PPS are fond of saying, "You are never finished."

1. Plaza de la Constitución de Oaxaca, Oaxaca City, Mexico

Commonly referred to as Oaxaca's zócalo, this plaza is the heart of a UNESCO World Heritage Site and an exceptionally sociable place. That is to say, it was a sociable place until April of this year, when workers with jackhammers started tearing up sections of the zócalo in preparation for a wholly unnecessary renovation.

Not all renovations are bad of course -- a 1974 re-design closed the zócalo to traffic and greatly improved it -- but the current changes are being implemented without any prior public consultation. The project was not presented to local residents until the day bulldozers arrived, and the process has remained frustratingly opaque ever since. The government has not been forthcoming with specific details of the renovation, though it is known that the park's popular imported trees were slated to be replaced by native species. Massive protests have swayed officials not to replace the trees until they die or become diseased, but no one is sure what sort of place the zócalo will be after the renovation wraps up.

2. Bryant Park, New York, NY

This heavily-used Midtown Manhattan park, located directly behind the New York Public Library, is now a favorite lunch spot for nearby office workers and rest stop for weary tourists. It's hard to believe now that in the 1980s it was transformed from an open air drug market to one of the city's most beloved gathering spots--a project in which PPS played a prominent role. Bryant Park's very success, however, has brought with it a new kind of threat: encroachment from private interests. For two months each year--once in February and once in September--the park's lush green lawn is not available to the public, as tents for the "Mercedes-Benz New York Fashion Week" swallow it up. At other times, the lawn has been taken over by the Ringling Brothers and Barnum & Bailey Circus, and, as we wrote about last year, VIP political shindigs.

Appropriation of this public space by private interests has come at considerable expense to everyday users, who find themselves shut off from what has been described as "the crown jewel of Manhattan." The managers of a place as beloved as Bryant Park should take pains to keep it available to all of its constituents all of the time. Almost all other privately managed civic squares in the U.S. and Europe either do not allow private events or ensure that the impact of such events remains negligible. No excuse can justify the continued practice of fencing off Bryant Park for events where only ticket holders can get inside.

3. Kungstradgarden, Stockholm, Sweden

Located in the heart of Stockholm, Kungstradgarden has had many incarnations, from royal garden to army drill-ground to lush public park. In its current form the park serves as a cautionary tale for places like Oaxaca's zócalo: It is a re-design gone awry. For years Kungstradgarden had an extremely open and flexible layout, and the park's managers took full advantage of this asset. The park played host to countless events and seasonal activities, from big performances to friendly one-on-one games of chess and ping pong.

A 1998 re-design of Kungstradgarden introduced made some of its spaces more inflexible and rigid. The garden was redesigned in 1998, and the resulting layout is much more rigid. Many of the small scale activities are no longer possible. Also scrapped in the redesign was an innovative demonstration playground featuring the latest designs for children's play equipment. Though Kungstradgarden remains popular because of its prime location in the heart of Stockholm, it is a shell of the place it once was.

4. Times Square, New York, NY

Times Square is still the center of Manhattan's theater district, but it is no longer the vibrant, enthralling public place that many Americans picture when thinking about the heart of New York. The area has long had problems, but the nature of the threat has changed in recent years. Once equated with sleazy adult theaters and peep shows, the area experienced a rebirth in the 1990s. With the new crowds came a different kind of threat: a lack of space provided for pedestrians. In today's Times Square, people are squeezed out into the street at every corner, often brushing dangerously close to traffic. You could say Times Square is a victim of its own success.

With vast numbers of office workers and tourists walking around Times Square amidst rivers of auto traffic, more space needs to be dedicated to pedestrian use. A thoughtful redistribution of space, with an eye toward improved pedestrian conditions and better sidewalk amenities, could turn Times Square into the thrilling, quintessential Manhattan place that now exists mainly in people's imaginations. Thankfully, the New York City Department of Transportation has allocated 15% more pedestrian space, and is working with the non-profit Times Square Alliance to study ways to add even more space. But until improvements are applied to the entirety of Times Square, it is bound to be a disappointment for tourists and an aggravating headache for New Yorkers.

5. Your Local Shops

All across the continent, from small town Main Streets to hip urban neighborhoods, independent businesses are struggling to stay afloat in the face of rampant chain store/big box expansion. While not all local businesses are great places and not all chains soulless purveyors of strip malls, on the whole a business owned by someone living in your community is likely to be a better neighbor. They tend to make use of existing storefronts rather than cookie-cutter buildings and parking lot configurations dreamed up in some faraway corporate headquarters and imposed on the neighborhood. They are also more likely to contribute to life in the place, helping buy uniforms for the local Little League or starting a Business Improvement District. The entrepreneurial impulse in Americans is strong and many folks dream of opening their own shop; it's up to the rest of us to support them if we truly care about the life of our communities.