Walkability is an urban quality indicator that is gaining increased attention because of its relationship to sustainability. Walkability refers to the set of incentives an urban space offers to encourage walking. More incentives mean higher walkability, hence more sustainable urban planning. This paper presents a geospatial approach to quantify the walkability of an urban space, based on physical indicators that can be layered in a GIS system. Preliminary results show good performance of the approach on the global level. However, further research is recommended to enhance performance at the local level.