Green space has long been assumed to have health benefits, including physical health. However, until recently, few long-term data have existed to show the mental health benefits of green space. Part of the research problem is most data collected on mental health is rarely georeferenced. A recent large-scale study in Denmark, however, combined historical Landsat satellite data and a survey that recorded mental health benefits to respondents to analyze the relationship between green space and mental health.
Analyzing Satellite Imagery to Map Green Space
In the study, researchers used free Landsat data that was of relatively higher resolution than MODIS data and also had covered Denmark between 1985 and 2003. The Danish Civil Registration system also allowed people to be recorded as to where they lived across that period, giving a rare opportunity to see how mental health has changed over a long period. This allowed researchers to link mental health responses, satellite imagery showing where green spaces were, and where people lived to make a link between mental health benefits and green space.
The study is the largest study, with about 940,000 tracked over the study period, to look at mental health in a GIS approach and to link mental health benefits with green space. The study showed that people who did not live in areas with minimal green space had up to a 55% greater chance of developing a range of psychiatric disorders that included depression, anxiety, and various substance abuses. This was even the case with other factors, such as family history or socio-economic level, were controlled for in the study.
The Link Between Mental Health and Green Space Exposure
In many ways, the study is similar to what has been demonstrated before. Similarly, in Wisconsin in the US it was shown that mental health improves with more green space exposure. In particular, anxiety, depression, and stress were all significantly reduced when green space was near where one lived, even if various socio-economic and other factors are controlled for.
Other studies use modern data collection and GIS measurements to determine distances people who live near green space, or even public open spaces, have to be in order to receive the most benefits from such spaces.
In Australia, a national study linking residential mental well being and location to green spaces or public open spaces showed that residents who lived within 400 m of such spaces benefited the most, including both mental and physical health. In effect, these findings largely echo the much larger Danish study and the study in Wisconsin.
Another study in Spain also quantified the normalized difference vegetation index (NDVI) values from imagery such as Landsat to demonstrate which scores of NDVI produced the best mental health benefits. For mental health, within 100 meters of a green space produced the highest mental health results, while for physical activity it was found to be about 500 meters.
High NDVI values showed that a green space was well developed and such spaces generally had the most positive results from respondents on their physical and mental well being. Overall, not only is living near a green space important for mental health but if that green space is substantial and is healthy then the benefits are even better. 
Green space provides many benefits to residents. Increasingly, studies from different locations are showing that those benefits can be profound, with long-term mental health effects shaped by how closely we might live near green space areas. Most results agree that living near green space is likely to diminish major mental health problems such as anxiety, depression, substance abuse, and stress.
 For more on the Landsat study that used historical data and a geolocated survey to track mental health benefits of green space, see: Engemann, Kristine, Carsten Bøcker Pedersen, Lars Arge, Constantinos Tsirogiannis, Preben Bo Mortensen, and Jens-Christian Svenning. 2019. “Residential Green Space in Childhood Is Associated with Lower Risk of Psychiatric Disorders from Adolescence into Adulthood.” Proceedings of the National Academy of Sciences116 (11): 5188–93. https://doi.org/10.1073/pnas.1807504116..
 For more on a corroborating result to the Engemann et al. 2019 study, see: Beyer, Kirsten, Andrea Kaltenbach, Aniko Szabo, Sandra Bogar, F. Nieto, and Kristen Malecki. 2014. “Exposure to Neighborhood Green Space and Mental Health: Evidence from the Survey of the Health of Wisconsin.” International Journal of Environmental Research and Public Health11 (3): 3453–72. https://doi.org/10.3390/ijerph110303453.
 For more on the Australia study that showed the distance people had to live near an open space or green space to obtain the greatest benefits, see: Hooper, Paula, Bryan Boruff, Bridget Beesley, Hannah Badland, and Billie Giles-Corti. 2018. “Testing Spatial Measures of Public Open Space Planning Standards with Walking and Physical Activity Health Outcomes: Findings from the Australian National Liveability Study.” Landscape and Urban Planning171 (March): 57–67. https://doi.org/10.1016/j.landurbplan.2017.12.001.
 For more on the study in Spain regarding green space and the use of NDVI for mental health, see: Su, Jason G., Payam Dadvand, Mark J. Nieuwenhuijsen, Xavier Bartoll, and Michael Jerrett. 2019. “Associations of Green Space Metrics with Health and Behavior Outcomes at Different Buffer Sizes and Remote Sensing Sensor Resolutions.” Environment International126 (May): 162–70. https://doi.org/10.1016/j.envint.2019.02.008.