Identification, spatial distribution, and associated factors of urban protected areas in China.

The increasing proximity between protected areas (PAs) and urban areas, which can lead to urban protected areas (UPAs), is now commonplace. Use of Euclidean distance to measure the distance between PAs and cities has not correctly portrayed the spatial relationship between PAs and cities. We devised an isochronous circle model to accurately measure the distance between 2706 national PAs in 5 categories and 2844 cities in China based on human accessibility to identify urban human activity-influenced protected areas (UHAIPAs) and to quantitatively analyze their distribution patterns and relationships with China's economy, population distribution patterns, and urban development indicators.