colour in the urban environment: a tool for the chromatic analysis of spatial coherence

Colour is an essential component of urban landscapes that inform us about the status and history of a place, through relations of dominance, integration or uniformity that can be observed between its built components. It can be shown that many traditional cities appear to be « chromatically polynuclear » in Europe and that each epoch, each type of urban area, each city is characterized by its own colour palette, which can be more or less homogeneous. Still the urban mutations observed in the second part of the 20th century generated a significant increase in the entropy of contemporary extentions of cities, which induced a loss of meaning and coherence by dislocating permanent structures set up in the past that maintained some integrity of urban landscapes. City entrances for instance, where old buildings mix with commercial equipment, show an unprecedented heterogeneity in their colour palettes. Few studies have focused on the description of these emerging configurations. Their complexity both in formal and chromatic aspects is certainly a difficulty from the perspective of their characterization. This can be explained by the lack of tools for an objective analysis of colour palettes in an urban environment.
Given this lack of both affordable and reliable assessment method of colour that has been observed in the field of urban design, the research presents the implementation of a tool that can be used to
characterize chromatic attributes of an urban area. The challenge is to provide statistical and
quantitative answers to these questions: how is colour organized, how does it develop its own structure in the city? How can colour appear as an indicator of homogeneity and spatial coherence?
As colour can be represented in a tri-dimensional space, we use a k-means statistical clustering
technique, based on a data partitioning algorithm, to produce a chromatic classification of building
facades. Once the chromatic categories are defined through the developed assessment method, the
question of spatial coherence is investigated using Shannon entropy. Our method was tested through an application to several urban fragments of the city of Liège (Belgium) and the research highlights the differences between historic urban areas (historic center, 19th century developments) with new urban configurations (city entrances, commercial and periurban zones).