Most of existing computer methods to analyse the perception of the open spaces do not consider the Gibsonian motion perspective , i.e.,the gradual changes in the visual field in the rate of displacement. This paper describes a new approach considering this motion perspective to analyse paths and routes in urban environments. Based on Teller 's spherical metric, it proposes to use the skeletonisation as a way to trace the variations of the sky shape between successive views. It is thereby possible to structure the route into sequences,according to its potential interest in the urban environment.