Metropolitan landscapes typically are patchworks of urban land use and open space. But metric geography and people¿s subjective perception of how green their neighbourhood is may divert. What looks appealing on a map may on the ground (and thus psychologically) turns out to be quite different. Main infrastructure blocks views, adds noise and prevents people from actually accessing the open space near to their home. In other words, although people may live near to open space, because of low permeability their actual daily sphere of activity may be less varied or further away than expected. In a growing and intensifying urban network, main arterials may be added or upgraded. For the sake of sustainability in terms of social well-being, access to open space, with its evident positive impacts on security, relaxation and health, needs to be taken into consideration continuously. However, proper modelling of permeability fails, making it tempting to leave this aspect behind altogether. Building on earlier work on compartimentation of people¿s physical environment, this paper presents a first attempt to model the permeability of open space by urban residents.@en