Introduction
Urban facades are not merely architectural envelopes; they are the visible face of cities and powerful carriers of cultural identity, economic growth, and social meaning. In traditional compact cities, facades reflect centuries of accumulated history while simultaneously facing the pressures of modernization and globalization. The conflict between traditional urban aesthetics and modern infill projects often disrupts the coherence of historical landscapes, producing fragmented urban identities.
To address these challenges, contemporary urban studies emphasize infill design, which refers to the development of vacant or underutilized plots within established city fabrics. Infill design is particularly critical in compact cities such as Tabriz, where historical districts coexist with rapid urban expansion. This essay expands on the original article Investigating Characteristics of Infill Design for Urban Facades: A Case Study in Tabriz, elaborating on its theoretical foundations, methodologies, and implications for urban planning.
The focus here is not only on empirical analysis but also on situating the study within a broader academic discourse on isovist science, integral calculus in spatial analysis, urban morphology, and facade identity.
Traditional Compact Cities and Urban Identity
Traditional compact cities, such as Tabriz, are characterized by:
Dense, mixed-use development
Walkable streets and strong pedestrian culture
Interconnected neighborhoods with historical layers
Cultural and social vibrancy rooted in public spaces
These environments encourage sustainability by reducing the reliance on extensive transportation infrastructure. Moreover, they embody a sense of belonging, where community identity is tied to the built form. Yet, as globalization introduces contemporary materials and construction methods, facades in such cities often experience disruption. This results in a visual discontinuity between historic cores and newer interventions.
The Role of Infill Design in Urban Façades
Infill design seeks to harmonize new construction with existing urban fabric. When properly implemented, it offers:
Enhanced aesthetics – by aligning with surrounding architectural language.
Sustainability – by reusing land and reducing urban sprawl.
Cultural continuity – by respecting historical forms while accommodating modern needs.
Economic growth – by raising property values and stimulating investment.
The challenge lies in defining measurable standards for harmony. While aesthetic guidelines exist in many cities, few studies have developed quantitative frameworks to evaluate infill design.
Isovist Science and Urban Perception
At the core of this research lies the isovist concept. An isovist represents all the points visible from a specific vantage point, bounded by obstructions. It quantifies visibility in terms of area, openness, perimeter, and visual complexity.
In urban design, isovists allow researchers to model how pedestrians perceive facades and cityscapes. When combined with computational models, isovist analysis can evaluate:
How much of a façade is visible from certain distances.
The balance between open space and built mass.
The degree of variation in vertical and horizontal elements.
The perceptual legibility of urban environments.
In the Tabriz case study, 3D isovist analysis and 2D integral calculus were used to capture both the quantitative and perceptual dimensions of facades.
Literature Review Expansion
Historically, scholars from different disciplines have addressed visual perception in cities:
Tandy (1967) first applied visibility studies in landscape analysis.
Benedikt (1979) formally introduced the isovist concept, establishing it as a measurable field in architectural research.
Kevin Lynch (1960) emphasized visibility and legibility in his seminal work The Image of the City, highlighting elements such as paths, edges, districts, nodes, and landmarks.
Batty (2001) extended isovist studies to urban morphology, demonstrating their role in shaping spatial cognition.
Kim et al. (2019) and Krukar et al. (2020) advanced 3D isovists, enhancing accuracy by accounting for vertical perspectives.
Asgharzadeh et al. (2012) explored the emotional dimension of visibility, linking oppressive or welcoming street experiences to façade openness.
Despite these advancements, very few studies have explicitly addressed infill design in traditional compact cities through the lens of isovist science. The Tabriz study fills this gap by introducing a mathematical model for infill design index (IDF), integrating both geometry and perception.
Methodology Expanded
Case Study: Tabriz
The chosen case is the Asia Insurance building in Tabriz, strategically located near Saat Square, a major urban landmark. The site is highly visible, positioned at the intersection of historical and functional urban zones. The building’s surroundings include educational facilities, hospitals, commercial centers, and municipal offices, making it an ideal microcosm of Tabriz’s urban complexity.
Research Stages
The study followed four major stages:
Case selection – based on Lynch’s urban gestalt principles.
Agent-based modeling – to simulate interactions between adjacent facades and the case study.
Integral and isovist analysis – applying mathematical models to quantify visibility and openness.
Simulation and survey – presenting 33 rendered façade variations to 74 random pedestrians for evaluation.
Mathematical Modeling
The infill design index (IDF) was derived using integral functions representing openness, façade components, and observer’s perspective. Equations quantified the contributions of:
Background (mass)
Horizontal lines
Vertical lines
Openings
The final golden ratio 40:11:2 emerged as the optimal proportion between façade surface, horizontal, and vertical elements.
Findings and Results
The simulations and surveys yielded several significant results:
Optimal façade proportion – Respondents preferred designs where approximately 40% of the observer’s view was façade, 11% horizontal lines, and 2% vertical lines.
Openness balance – The desirable ratio of openness to façade visibility was about 53:40, ensuring neither excessive voids nor overwhelming solidity.
Adjacency consideration – Respondents valued coherence between the studied building and its neighbors, confirming Lynch’s emphasis on urban gestalt.
Cultural and environmental adaptation – Incorporating greenery into horizontal elements was perceived positively, aligning with local climate conditions.
These findings indicate that quantitative design rules can capture qualitative perceptions, providing urban planners with measurable criteria.
Discussion
Urban Identity
The study highlights the fragile balance between modern interventions and traditional character. Infill design, when guided by scientific ratios, can act as a mediator between preservation and development.
Methodological Contributions
Unlike previous studies, this research integrates:
Mathematics (integral calculus)
Visibility analysis (isovist science)
Human-centered evaluation (Likert surveys)
This mixed-method approach demonstrates how urban perception can be quantified without losing its subjective richness.
Limitations
The study relied heavily on quantitative variables; qualitative factors such as rhythm, materiality, and symbolic meaning require further exploration.
The use of mathematical formulas, though rigorous, can be time-intensive. Developing software tools for automatic IDF calculation is a logical next step.
The findings are localized to Tabriz; testing them in culturally similar cities such as Istanbul would validate their universality.
Broader Implications
For Urban Designers
The 40:11:2 ratio provides a practical guideline for façade composition, balancing solidity and openness. Designers can adopt this rule when working in sensitive historical contexts.
For Policy Makers
Urban façade regulations often emphasize aesthetic language without measurable standards. The IDF index offers a scientific framework for decision-making, reducing subjective disputes in façade approval processes.
For Cultural Heritage
By aligning infill projects with perceptual and mathematical harmony, cities can preserve cultural identity while accommodating growth.
For Technology and Future Research
The integration of 3D isovist tools, VR simulations, and AI-based evaluations can expand the scope of infill design studies, enabling real-time analysis of urban interventions before they are built.
Conclusion
The expanded study of infill design in Tabriz illustrates how science and perception converge in urban design. By quantifying visibility and façade composition, the research introduces a golden ratio for urban facades (40:11:2), offering both practical and theoretical contributions.
The findings confirm that traditional compact cities require context-sensitive design solutions. Infill design should not be arbitrary but rather grounded in measurable harmony between façades, urban openness, and human perception.
In a world where cities constantly evolve, methodologies like isovist analysis and mathematical modeling provide urban designers, planners, and policy makers with tools to create environments that are both sustainable and culturally resonant.