So called “multishading masks” are obtained by combining together several shading masks computed for a series of sample points uniformly distributed over the open space under study. By superimposing these “multishading masks” with common sun-path diagrams, it is possible to assess which area fraction of an open space is exposed to sunlight during the different seasons and to verify if additional shading elements (e.g. trees) can improve users’s satisfaction. When combined with sky radiance distributions, the same “multishading masks” can also be used to quantify irradiance levels reaching open spaces.