The key aim of this paper is to develop a computational method for mapping architectural space used for visual openness analysis. We suggest that the result will offer possibilities for quantitative design analysis particularly on spatial quality influenced by architectural elements. The proposed method consists of two stages: determination of subdivided enclosed spaces and measuring quality using visual openness parameters on each subdivided enclosed space. We advise new approach to determine subdivided enclosed spaces on architectural plan by determining two factors: bounded space and circulation space. Computational procedures applied to analyse architectural plan and then determine map of subdivided enclosed space by analysing relationship of these two factors. The concept underlying this method is that architectural space is composed of subdivided enclosed spaces, which each of them have distinct physical properties and therefore become possible to develop mapping of evaluation regarding the quality of architectural space. Our finding on orthogonal architectural plan provides ranking index of subdivided enclosed spaces that could help for analysing spatial quality of architectural space.