Quantifying parks as preventive health assets using population-scale mobility data

Urban parks are promoted as preventive health assets, but cities lack park-level evidence linking real-world use to investment feasibility. Here we combine anonymized mobile-phone data covering 1.79 million park visits by 320,000 users with records for 4139 parks, land prices and population across Greater Tokyo. We estimate walking-related preventive health benefits and compare them with land, construction and maintenance costs in 2019 Japanese yen. We show that benefits decline with residential distance within about seven kilometres, while park type mainly changes their level. Returns are highly uneven and concentrated among small parks: about 16% of block parks recover costs within 20 years, whereas large destination parks rarely do so when only walking-related benefits are counted. Planning estimates suggest different siting strategies for the two smallest park classes. This framework offers cities a transparent way to compare projected walking-related health returns and screen investments under land and budget constraints.