A temporal gradient approach reveals similar infrastructure composition but marked density differences along the gradient in new and old built-up areas

To understand the impacts of environmental and socioeconomic changes on the sustainability of urban and rural landscapes, it is essential to quantify the landscape patterns along the urban-rural continuum. However, current characterizations of urbanization often rely on impervious surface patterns, overlooking the intensity and types of human activities within urban areas. We aimed to explore the pattern of human activities along the urban-rural gradient. Specifically, we examined how the density and types of human activities varied between the urban center and the urban fringe. We used social infrastructure to represent human activities, and mapbed the built-up areas of different ages as the urban-rural gradient. Then, we examined the density and composition of social infrastructure within different ages of built-up areas in Shenzhen. The density of social infrastructure decreased significantly along the gradient of the new and old built-up areas. The oldest built-up area had a density of 1,036 per km², while the newest one had only 75 per km². The composition of social infrastructure was similar along the urban-rural gradient. However, after the turning point around 2010, the density and composition of social infrastructure changed slightly. The density of social infrastructure was no longer declines, but fluctuated, and the composition of social infrastructure was no longer constant as the proportion of accommodation services increased. This study revealed human activity patterns along the urban-rural gradient, enhancing our understanding of urbanization, and offering valuable insights for sustainable landscape management.