Exploring Urban Coherence through Fractality, Connectivity, and Arteriality of the Urban Street Network: Comparative Study of Five Medium-Sized Algerian Cities

Urban coherence is recognized in the literature as an essential property of a sustainable and virtuous urban form. Although remaining rather vague and dispersed, urban coherence seems to be often apprehended through the interweaving and interrelation of scales in a complex system. This exploratory work aims to deepen the notion of urban coherence by studying the street network hierarchy and connectivity in relation to an essential and identifiable property of networks, known as arteriality. It indicates the tendency of the most important streets in the network to form a continuous whole. Arteriality guarantees optimal circulation and legibility within a street network. In the first step, a literature review was conducted to identify indicators of urban coherence related to the street network. Subsequently, an evaluation of urban coherence was proposed based on three aspects: the fractality of the street network and its correspondence with a power law, the connectivity of the primary street network, and the arteriality of the street network. This conceptual framework was then tested on five cities’ street networks belonging to five medium-sized Algerian cities. The results showed that all the cities studied have a certain urban coherence due to a similar internal structuring. However, from a relative point of view, there were notable differences that can be seen when comparing the cities. It also emerged that the indicators chosen to evaluate urban coherence show a certain regularity within the same city, which may confirm their relevance.

Urban coherence is an important quality for a sustainable and well-designed city; however, it is not a concept very clearly defined in the literature. A simple definition of it can be “how different parts of a city work together in a complex way.” This study tries to better understand how well a city's streets are hierarchically organized by looking at how they connect to each other, especially the most important ones. A particular property of the street networks called arteriality, which means the tendency of the most important streets in the network to form a continuous whole, was developed. The urban coherence was evaluated based on three aspects: the way the streets are hierarchically arranged, how connected they are, and how arterial they are. The study looked at five medium-sized cities in Algeria and found that they all have some level of urban coherence, but there are also notable differences between them. The chosen indicators to measure urban coherence showed a good consistency within each city, which may suggest that they are relevant. This work has important theoretical implications regarding the hierarchical organization required for a functional street network. Also, it can be further used by urban planners to design better street networks for new areas and improve existing ones.