Measuring Visual Pollution in Individual Housing in Bou Saâda, Algeria: A Comparative Study of Four Urban Patterns Using the Analytic Hierarchy Process (AHP)

Abstract

Visual pollution is an escalating urban-environmental challenge that has attracted growing scholarly attention in urban planning and built environment research, particularly in developing cities undergoing rapid and largely unregulated spatial transformation. This study measures the variation in visual pollution levels across four residential neighborhoods representing distinct urban patterns in the semi-arid context of Bou Saâda, Algeria: the Traditional Quarter (Ksar), the Colonial District (Le Plateau), the Modern Planned Settlement (110 Dwellings), and the Informal Settlement (Sidi Slimane). The Multi-Criteria Analytic Hierarchy Process (AHP) was applied following Saaty's protocol, complemented by a systematic field survey and in-depth expert interviews with specialists in urbanism and environmental planning.A comprehensive hierarchical evaluation framework was developed, comprising 30 criteria—10 shared across all patterns and 20 pattern-specific—alongside 275 indicators assessed on a 0–5 scale. The total observed visual pollution reached 1,975 points. Results revealed a pronounced divergence among the four patterns: the Informal Settlement ranked highest by a substantial margin (711 points, 36.00%), followed by the Traditional Quarter (439 points, 22.23%), the Planned Settlement (416 points, 21.06%), and the Colonial District (409 points, 20.71%). The absence of green spaces emerged as the most heavily weighted shared criterion (14.03%), followed by unfinished buildings (9.83%). Pearson correlation analysis further demonstrated that visual pollution operates as a tightly interconnected structural system, with correlation coefficients exceeding r = 0.80 in the majority of cases. The study concludes with a phased, evidence-based roadmap for improving visual landscape quality in comparable Algerian cities.