Rapid urbanisation in Southeast Asia has weakened spatial linkages between peri-urban food production and urban consumption. Although food miles are widely used as environmental indicators, their application in spatial planning remains limited. This study operationalises the Weighted Average Source Distance (WASD) within a reproducible geospatial workflow to analyse distance-quantity relationships in peri-urban food distribution. Using a 2024 post-pandemic survey dataset from 48 farms and 261 vegetable-flow routes in Thawi Watthana District, Bangkok, the analysis reveals a distribution system characterised by long-distance transport: 75% of production occurs beyond a 30 km radius, accounting for 80% of the overall WASD (38.5 km), despite the geographic proximity of production to urban demand. To support planning-oriented interpretation, distribution flows are analytically structured into distance-based categories representing near-city (≤15 km), mid-range (15-30 km), and metropolitan-scale (>30 km) supply connections. This distance-tiered spatial analysis demonstrates how transport intensity is unevenly concentrated across space and highlights structural mismatches between geographic proximity and prevailing distribution practices. Validation in Bangkok suggests that this geospatial framework can support spatial diagnosis of food-system vulnerabilities in other rapidly urbanising metropolitan regions.