This report explains the development of a GIS-based decision-support tool that identifies candidate car park sites for potential conversion into new urban parks. It uses openly available spatial and statistical datasets, the tool combines network-based accessibility modelling with multi-criteria scoring based on demand, underserved demand, distance from existing green spaces, site size and flood suitability. Case studies in Cardiff and Swansea show that the tool can be used to identify locations that would improve park accessibility under different walkability thresholds and planning priorities. Comparative testing showed that the multi-criteria method outperformed simple size-only and distance-only baseline methods. The findings show that open data can support transparent urban planning analysis, but the outputs should be treated as data-driven planning evidence rather than a replacement for professional judgement.