Given the importance of competition in the retail sector, this research builds on spatial interaction theory to develop the competition index (CI). For this, geographic information systems (GIS) and the analytic hierarchy process (AHP) were used. AHP results reveal that key factors to assess com-petitors relate to location and branding. The proposed method was tested by evaluating 45 supermarkets in the city of Castellón (Spain). Using this method, sales targets can be adapted to each outlet’s individual circumstances.