Given the following passage  "In its 2013 ParkScore ranking, The Trust for Public Land reported that the park system in New York City was the second best park system among the 50 most populous U.S. cities, behind the park system of Minneapolis. ParkScore ranks urban park systems by a formula that analyzes median park size, park acres as percent of city area, the percent of city residents within a half-mile of a park, spending of park services per resident, and the number of playgrounds per 10,000 residents.",  answer the following question. Note that the answer is present within the text.  Question: What does ParkScore's unique formula seek to measure?
urban park systems