One of the main objectives of geographical information systems is to support the process of decision making. Spatial modeling can be a useful tool to provide such support also for the analyses of general security, including preventing illegal border crossing (immigration and smuggling). The paper presents a spatial model to estimate the level of border permeability. The model is based on Border Permeability Index (BPI) concept as presented by Stephenne and Pesaresi (2006). The valuation of the border and the borderland was done with the use of only physiographic factors. There was analyzed the attractiveness of the border-crossing way for an adult person who plans to cross it illegally on foot in summertime. The model comprises two elements. ‚Walk’ describes the attractiveness of the area for fast covering the distances on foot. ‚Hide’ describes the attractiveness of the area to stay unseen. The data for the analyses was provided by V-Map 2, archival topographic maps and mid-resolution satellite images (Landsat 7 ETM+). The data used in the presented spatial modeling was much more detailed in comparison with the data used by Stephenne and Pesaresi (2006). This fact resulted in a completely different attitude to the model construction and, consequently, in a different definition of the Border Permeability Index (BPI). The model was applied to assess the border permeability between Poland and Ukraine. It comprises a part of the G-MOSAIC (GMES services for Management of Operations, Situation Awareness and Intelligence for Regional Crises ) a project conducted by CBK PAN.