This is the fifth and final part of a series on urban design gone wrong. For part one, click here. For part two, click here. For part three, click here. For part four, click here.

Ever since someone described parks as the "lungs of the city," cities have been competing to declare themselves as "green" by allocating space for public parks in urban redevelopment initiatives.

This race to boost the percentage of green space for city brochures is typical of this age of "competitive cities." In many ways it is welcome — parks have even been shown to not only make us healthier but even make us smarter. But parks should not be judged on quantity, but quality.

In this final instalment of the series on "getting urban design wrong," I propose six guidelines for good parks that help us begin to think of parks as an urban design challenge, and to right some of our wrongs.

1. Design parks that people use

"Build it and they will come" is not a good starting point for building parks. You cannot merely designate a space, lay out a green carpet to visitors and wait for the park to come to life.

A good park guides visitors to what they can do in the space zones might be set aside for play, screening outdoor films, theatre, picnics, nature trails, or simply sitting and chatting.

The reason that the National Mall in Washington D.C. earned its place in the Project for Public Spaces' "Hall of Shame" is because it does not provide even basic amenities like places to sit that will draw visitors in. With few focal points, landmarks or events, it becomes merely a corridor to pass through, despite its enviable location.

In contrast, Chile’s celebrated Children’s Bicentennial Park has a clear idea of how it wants to be used it incorporates a "wild space" for children that bucks the trend of formulaic template playgrounds and provides space where they can make dens and play in nature.

All of the above must of course be based on asking who lives in the neighborhood, and what those people want from their park. Increasingly, parks are trying to make themselves more useable to the growing demographic of people over 60 years old with specially designed outdoor gyms or socializing spaces for the elderly.

2. Make sure it 'speaks' to the rest of the city

Often the green space in our cities exists, but it is ignored and underused because it relates poorly to its surroundings.

Parks do not exist in isolation. In many cities particularly those heavily redeveloped in the 1960s the buildings surrounding the green spaces do not create a "frame" for the park, but instead turn away from it.

Demanding "active frontages" along the edges of the park can help bring both life and a sense of security. Looking at the street life that surrounds somewhere like Central Park shows how important what happens on the edges of a park is to the success of the park itself given a boost by ongoing pedestrianization initiatives.

This is where like many other parks built from scratch Parc Andre Citroen in Paris falls down. Despite large sums being spent, the park floats in its surroundings rather than successfully stitching itself together with them. We expect better of Paris.

3. Balance nature and human activity

The very notion that parks can act as the "lungs of the city" and havens of biodiversity is appealing. But we have to be very clear about why we are building a park.

With any "green infrastructure," we tend to forget that there is always a trade-off between catering for humans and catering for nature lighting might be fantastic for creating a safer environment for humans, but not so welcome for the plants they are enjoying.

Similarly, as London’s Royal Parks have been forced to increasingly commercialize, concerns have been raised that the outdoor cinema events held more and more often in the parks are more popular with London’s homo sapiens than with its bat population.

An urban park is no nature reserve, but ideally an amenity for humans that aims to "tread lightly" on the surrounding ecosystems and perhaps give them a boost. Getting the balance right is tricky.

4. Bigger is not always more beautiful

Historically parks have been "gifted" to cities. In London this was by the royal family and aristocratic classes, while in the U.S. this has more often taken the form of "gifts" by wealthy philanthropists with some suggesting we are entering a new "golden age of parks philanthropy."

However, one criticism of our current approach is that it creates a love affair with expansive "signature" parks over smaller local "pocket parks" that tend to serve neighborhoods in less wealthy areas, particularly for families. An initiative to better redistribute philanthropists' funds to less spectacular parks in the U.S. has proved very controversial.

5. Think about how who is going to maintain them

With dwindling public funding for our public spaces across the West, handing parks over to private developers is becoming one of the only viable mechanisms for keeping them trim. But these privately owned public spaces come with their own challenges, and philosophical dilemmas over unintended consequences.

Thinking carefully about maintenance strategies and park design from the outset too can be key in avoiding impressive but "high-maintenance" parks.

6. Create a park to remember

Finally the most elusive goal of all is making the park memorable instilling it with an identity. Identikit parks might fulfill the "green quota," but humans won’t necessarily want to spend their Sunday in them.

Landscape architect Kim Mathews does this by scanning for "hooks" in the history of the environment and integrating them into the design. Those hooks might begin with surrounding industrial heritage, or more radical designs that attempt to mirror the diverse makeup of the surrounding neighborhood like this award-winning park in Copenhagen.