Partial isovists fields are useful methods to analyze the urban morphology taking into account the visual perception of the pedestrian. However, as previous studies involve a constant visual aperture angle all along the pathway, this paper presents an adaptative method of aperture angular variation according to urban morphology properties. Aperture angle increasing, nearby a square or at roads junction, or decreasing within a canyon street should improve the micro-behavior visual perception in our simulations. With showing that traditional isovist's shape indicators are not well adapted to achieve urban environmental properties, the aim of this paper is to present this new methodology based on a statistics standardized moment called Kurtosis. Our results show that this method could be used to define a surrounding space typology, one step more towards the modeling of visual dynamics.