Many American cities are making ambitious plans to remake their public realms, reinvesting in parks, libraries, and other civic assets. For the last two years at PennPraxis, we've been studying these plans, including the ways that cities maintain, or fail to maintain, their public spaces. It may not seem fun or sexy, but maintenance is radically progressive, sustainable, and even subversive — challenging our societal preference to value new things more than things we inherit. To succeed in making cities more equitable and more sustainable, cities need to be better maintainers.

Cities are prone to over-invest in new, shiny spaces and fail to maintain the spaces they've already got. But innovative new public spaces can't solve complex urban problems by themselves; new central parks, pop-ups, and tactical urbanism contribute a lot, but they're only half the picture.

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Maintenance, preservation, and adaptation have to be a serious part of any city's public asset strategy. Indeed, reinvesting is one of the big emerging stories in urbanism in the last generation: rediscovering the value, civic energy, and pleasure packed in to collections of cities' shared public spaces. Or, as we like to think of it, "civic infrastructure."

And the very idea of infrastructure is not just building new, elaborate systems of parks, buildings, roads, and pipes, but running them over time, reinvesting in them, managing them  — that is, maintaining them.

Maintaining civic infrastructure builds trust and pride, engages workers and supports local economic development, reduces waste, and produces public benefits such as educational life of libraries, encounters with nature in parks, and the freedom to gather in public spaces. Maintenance also accomplishes other things: creates jobs and economic opportunity, rallies communities around a sense of "ownership," teaches us about nature, and makes society and its infrastructure more resilient.

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Based on our research, we see two problems facing cities as they reinvest in their public realms: finding the money to keep maintaining; and pushing back on the reputation of maintenance as uncreative or unsexy. The two are related. Building new and maintaining are not an either/or choice; cities need new stuff, too. And simply because maintenance is less visible, it suffers in comparison with making new things in our look-at-me culture.

Maintenance is at the heart of Philadelphia's Rebuild program: a $500-million effort to maintain and improve the parks, libraries, and rec centers we've already invested in. It is the biggest effort in the country to build a better city simply, elegantly, efficiently, equitably.  Money and reputation remain big barriers: The city and its partners have a plan for the financing, but what about repairing the reputation of maintaining and repairing?

Maintenance is not just drudgery. Simple acts of maintaining can lead to bigger, more transformative and visible changes.

It can be inspiring, as in the case  Tyrone Mullins, a San Francisco resident and entrepreneur behind the success story of Buchanan Mall, where Mullins built a recycling business (Green Streets) focused on maintaining his neighborhood. Green Streets catalyzed local residents, attracted new partners from around the city, and invested the hard work of building and defending community by designing and maintaining their public spaces.

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Here in Philly, the solution to long-standing repair backlogs at pools, parks, and libraries doesn't rest on any single desk.  As the city makes big investments, it is also working to have these investments create jobs and economic opportunities for those who need them most. Staff and volunteers provide immense amounts of labor through park stewardship, community gardening, and recreation center organizing efforts – supported by a network of public agencies and nonprofits, including the city's Parks and Recreation Department, Fairmount Park Conservancy, and the Pennsylvania Horticultural Society.

Wherever you see new places and visible change, remember that flashy new parks and buildings and "disruptive innovation" are not all a thriving city needs. When it comes to public space, straightforward acts of maintaining what we've inherited have to play a significant part of our collective work to build a more equitable and sustainable city.

Randall Mason is an associate professor at Penn's School of Design and senior fellow at PennPraxis. Elizabeth Greenspan is a senior researcher at PennPraxis.