Global geographical access to urban green spaces

Cities are growing faster than ever, and as they expand, the ground beneath our feet is increasingly covered by concrete and asphalt. These hard surfaces soak up the sun's heat during the day and release it slowly at night, creating a warm bubble over the city that makes life uncomfortable and dangerous for many people. In response, city planners and health experts have long argued that the solution lies in green spaces. Parks, gardens, and tree-lined streets do more than just look nice; they cool the air, encourage people to walk and exercise, and offer a mental respite from the noise and stress of urban life. The United Nations has even set a global goal for 2030, aiming to ensure that everyone, regardless of age or ability, has access to safe and inclusive green areas. But a critical question remains: just because a park exists on a map, does it actually mean a person can get there?

For years, the standard way to measure this access was simple geometry. Researchers would draw a circle around a park and count how many people lived inside that circle. This method, however, ignores the reality of walking. A park might be only a few hundred meters away in a straight line, but if a busy highway, a deep river, or a steep hill stands in the way, that short distance can become a long and difficult journey. Furthermore, not everyone walks at the same speed. A young adult can cover ground quickly, while an older person or someone with limited mobility might move much slower, shrinking the area they can reach in the same amount of time. Until now, no one had mapped these real-world walking conditions for cities around the entire world, leaving a gap in our understanding of who truly benefits from the green spaces we have.

A team of researchers from the University of Geneva has now filled that gap with a massive, detailed study covering 11,422 cities in 191 countries and territories. Instead of drawing simple circles, they built a digital model of the world's cities that accounts for the actual obstacles a pedestrian faces. They used high-resolution maps to see where roads, railways, rivers, and steep slopes exist, and they programmed the model to calculate how long it would take to walk from any point in a city to the nearest patch of green. Crucially, they ran these calculations twice for two different groups of people: those under 65 years old and those 65 and older. They also tested three different walking speeds to account for the natural variation in how fast people move, ensuring their results were not just a guess but a realistic estimate of human movement.

The researchers defined "green space" in two ways to see how the definition changes the story. Their first, stricter definition included only places designed for people to use, such as public parks, playgrounds, and recreation grounds. Their second, broader definition included any vegetated area, such as forests, meadows, and scrubland, even if they were not officially open to the public. This distinction proved vital. When they looked at the strict definition, they found that globally, only about 60 percent of people under 65 could reach a green space within a 15-minute walk. For those aged 65 and older, the number dropped to about 55 percent. If the goal was a very short, five-minute walk, the situation was much worse, with only about a quarter of the younger population and fewer than one in five older people able to reach a park in that time.

The study revealed that where you live matters more than how big your city is. The regions with the least access were South Asia and Sub-Saharan Africa, where many people live in dense urban areas with very few parks nearby. In contrast, North American cities generally had the highest access. The researchers also discovered that being a "megacity" with millions of residents did not automatically mean poor access. Some of the world's largest cities, like New York and Seoul, had excellent green space coverage, while others, like Lagos in Nigeria and Dhaka in Bangladesh, had very little. In Lagos, for instance, the strict definition showed that almost no one could reach a park in 15 minutes, but when the researchers included the broader, wilder green areas, the number jumped dramatically, showing that the type of green space available makes a huge difference in the statistics.

Perhaps the most surprising finding was that the amount of green space in a city does not guarantee that people can reach it. The researchers compared two cities, Nairobi and Bengaluru, which had nearly identical amounts of green land. Yet, in Bengaluru, 87 percent of the population could reach a green space in 15 minutes, while in Nairobi, only 32 percent could. The difference was not the total size of the parks, but how they were spread out. Bengaluru had many small parks scattered throughout the neighborhoods, while Nairobi had a few large parks that were far apart. This showed that a city can be full of greenery but still leave most of its residents without easy access if that greenery is not distributed where people live.

The study also highlighted a significant gap between generations. In almost every city they examined, older adults had much harder times reaching green spaces than younger people. On average, the share of older residents who could reach a park in 15 minutes was about 15 percentage points lower than that of younger residents. This gap was driven largely by walking speed; because older people walk slower, the area they can cover in a set time is smaller, and they are more likely to be cut off by barriers like busy streets or steep hills. This suggests that current urban planning often fails to consider the specific needs of the elderly, even though they are among the most vulnerable to heat and health risks.

Ultimately, this research provides a new, more realistic way to measure how green our cities really are for the people who live in them. It moves beyond simple counts of trees or parks to show who can actually get there and how long it takes. The findings suggest that to meet global goals for healthy cities, planners need to focus not just on planting more trees, but on ensuring those trees are close to where people live and are easy to reach for everyone, regardless of their age or ability. By understanding the true barriers to access, cities can start to design neighborhoods where the benefits of nature are available to all, not just a lucky few.