Identifying and assessing online food delivery swamps in major Chinese cities.

The rise of "online food delivery swamps," driven by digital platforms, raises important questions about how urban food delivery systems affect nutritional equality. To overcome the limitations of traditional methods that rely on store classifications and physical proximity, this study introduces a high-resolution framework integrating dish-level nutritional data with digital accessibility. Applying this to 254,642 vendors across ten major Chinese cities, our analysis reveals a widespread structural imbalance in the food environment, marked by an oversupply of energy, fat, and carbohydrates. Spatially, all cities exhibit a stark "core-oasis, periphery-swamp" pattern, exposing significant intra-urban inequality. We uncover a critical mismatch between the geographical extent of these swamps and the actual residential proximity to nutritionally imbalanced food supply, identifying distinct urban patterns from "extensive coverage-low residential exposure" to "high coverage-high residential exposure". Furthermore, we demonstrate that "food swamps" are not monolithic; instead, they comprise heterogeneous subtypes with unique nutritional deviation profiles. This study uncovers new dimensions of urban nutritional supply inequality in the digital era, providing evidence that may inform the development of food environment policies.