The Harmonic Ratios of Informality: Behind the colonial structural grid of Bab El Louk, downtown Cairo Part 2 Dissertation 2025 Youssef Altantawy American University in Cairo Cairo Egypt Bab El Louk, one of the oldest markets in Cairo, often dismissed as a decaying colonial remnant. This paper reframes it as a dynamic ecosystem of informal architectural intelligence. Challenging binary perceptions of order/disorder, this study reveals how vendors, materials, and spatial practices co- author resilience through everyday negotiation, adaptation, and care.Integrating Actor-Network Theory with culturally grounded frameworks such as sacred geometry and BioGeometry, the project decodes how informal interventions generate harmonious spatial coherence introducing the novel Psychogeometric Coherence Coefficient (PCC), a metric quantifying how stall dimensions, airflow patterns, and thermal adaptations unconsciously approximate mathematical harmony (e.g., Golden Ratio), translating embodied knowledge into measurable data.Through ethnographic fieldwork, archival timelines, and spatial mapping (1912–2025), the study documents Bab El Louk’s transformation from colonial grid to a palimpsest of quiet resistance. Findings reveal informality not as chaos but as positionally emergent order where relational governance and generational memory recalibrate space beyond state neglect. By centering informality as vernacular design agency, this work reframes urban resilience globally, advocating for policies that learn from, rather than erase, such sites of living heritage. Bab El Louk emerges as vital theory: an architecture authored through survival. Tutor(s) Momen El-Husseiny