Park advocates often talk in terms of per capita parkland standards. This takes the form of a statement like "there should be __ acres of parkland per capita". This seems to me like a problematic way of figuring out how to make great community park systems.
Why? First of all, the use of acres, instead of the metric unit, hectares (I'm, just saying there are 43,560 square feet in an acre and 10,000 square meters in a hectare, which seems better to work with?). But on a more serious note, area per capita parkland standards ignore the context they are in. Specifically they ignore the critical issue of population density and how urban, suburban and rural places work differently.
Urban places can't have as much parkland per capita as suburban and rural places (unless we figure out how to build parks into multi-story buildings). They just can't, otherwise they cease to be urban. Imagine Manhattan island in New York City, with all of its parkland, including majestic Central Park and its ring of high-rises. Dense urban places like these have a lot of people on a relatively small amount of land. All those people mean when you calculate park area / person you're dividing by a large number.
In suburbia and rural areas, lower densities mean that you're dividing by a relatively small number. Hence the metric is stacked against urbanism.
Many factors are important to park quality. Are parks distributed fairly? Can everybody access them, even if they don't own a car? In their context do they contribute to or detract from community safety and pedestrian life? Do they have the kinds of facilities (or lack thereof) that the community wants? Is the community's existing and planned park system financially sustainable?
Reducing the discussion to area per person is not only context insensitive, but also ignores all of these other factors. We should measure the adequacy of park space by grappling with the questions above and with another one: what percentage of a community's land should be parkland?
By this point it should be dawning that there are no easy answers.