Evaluating methodological approaches to urban park accessibility: a comparative analysis of statistical, network-based, and gravity measures in Quincy, Illinois

Imagine a city as a living map of opportunity, where the distance between a home and a park is not just a matter of miles, but of health, community, and fairness. For decades, urban planners have tried to measure this distance to ensure that every neighborhood, rich or poor, has a fair share of green space. They have long relied on simple tools: counting how many acres of park exist within a neighborhood's borders, or drawing a perfect circle around a home to see what falls inside. But these methods often miss the reality of how people actually move. A straight line on a map does not account for a busy highway, a missing sidewalk, or the fact that a large park might be right next door, yet its only real entrance is a mile away. In the real world, access is defined by the path you can actually walk or drive, not by the shortest distance as the crow flies.

This reality is the focus of a new study examining Quincy, Illinois, a mid-sized American city where parks are scattered and many residents rely on cars. Researchers set out to test whether the standard ways of measuring park access tell the true story of who can reach a green space and who cannot. They compared three different ways of looking at the map: a simple count of park space per neighborhood, a method that traces actual roads to see how far a person can walk or drive, and a complex model that weighs the size of the park against the number of people nearby. By running these different methods side-by-side, the team discovered that the choice of measurement tool changes the answer entirely. In a city where walking is difficult and driving is common, the method used to measure access determines which neighborhoods are labeled as underserved and which are considered well-served.

The study began by gathering detailed data on Quincy's 21 public parks, its road network, and its population. The researchers then applied three distinct approaches to the same data. The first approach was the traditional statistical method, which simply calculated how much park land existed within each census block, a small administrative area. This method is easy to use but assumes that people can only use parks inside their own neighborhood and that everyone has equal access regardless of how they travel. The second approach used network analysis, which traces the actual streets and sidewalks to calculate how far a person must travel to reach a park. This method tested two different travel modes: a one-kilometer walk, representing a short trip on foot, and a five-kilometer drive, representing a short trip by car. Crucially, the researchers also tested three different ways of defining where a park "is": at its geometric center, along its entire edge, or specifically at its actual entrances. The third approach was a gravity model, a more complex calculation that considers not just distance, but also the size of the park and the number of people living nearby, assuming that larger parks attract more visitors and that people are less likely to travel far for a small one.

When the researchers compared the results, the differences were stark. The simple statistical method showed a general picture of where parks were located, but it failed to capture the reality of travel. It suggested that some areas had good access simply because a park happened to be inside the neighborhood boundary, even if that park was cut off from the street by a fence or a highway. The network-based approach, which followed the actual roads, told a very different story. Under the one-kilometer walking limit, access was extremely low for most of the city, concentrated only in a few pockets where parks were close to homes and connected by sidewalks. However, when the same analysis was run for a five-kilometer drive, the picture changed dramatically. Almost the entire city became accessible, showing that in Quincy, the ability to drive is the primary factor determining whether a resident can reach a park.

The study also revealed that how a park is represented on the map matters significantly. Using the center of a park as the destination point often overestimated the distance people had to travel, especially for large or oddly shaped parks where the center might be deep inside the grounds, far from any road. Using the park's edge was slightly better, but the most accurate picture came from using the actual entrances. By mapping the specific points where a road meets a park gate or a parking lot, the researchers found that this method provided the most realistic view of access. It showed that some parks, while technically "near" a neighborhood, were functionally unreachable because there was no direct path to them.

Perhaps the most surprising finding concerned the complex gravity model. In cities with many parks and good walking infrastructure, this model works well, creating smooth maps of accessibility. But in Quincy, a city with few parks and a heavy reliance on cars, the model produced fragmented and confusing results. It created isolated "hot spots" of high accessibility near large parks, while ignoring the reality that people in other areas simply could not reach them. The researchers found that in low-supply environments, this model tends to exaggerate the importance of park size and population density, creating patterns that do not reflect how people actually move. The study concluded that for cities like Quincy, the network-based approach using actual entrances is the most reliable tool. It respects the reality of the road network and the specific constraints of walking versus driving.

The implications of these findings extend beyond the map of Quincy. The study suggests that for mid-sized, car-dependent American cities, planners must move away from simple counts and complex models that assume a well-connected world. Instead, they should focus on the actual paths people take. The research highlights that for those without cars—the elderly, children, and low-income families—access to parks is severely limited, not just by distance, but by the lack of safe walking routes. The study argues that to create truly equitable cities, planners need to use methods that reveal these hidden barriers. By understanding that a park is not accessible until there is a real path to its door, cities can make better decisions about where to build new parks and where to improve sidewalks, ensuring that green space is a reality for everyone, not just a statistic on a page.