From Urban Expansion to Urban Densification: A GIS-Based Assessment of Building Density Dynamics in Colombo District, Sri Lanka (1975–2025)

Abstract

Urbanization has transformed settlement patterns worldwide, leading many cities to shift from horizontal expansion to vertical development. Building density is a key variable for assessing urban growth patterns and urban densification. Colombo district, the main economic hub of Sri Lanka, has experienced rapid urban growth during the last few decades. However, despite the rapid pace of urbanization, long-term GIS-based assessments of building density remain limited in Sri Lankan. Therefore, this study aims to assess the spatio-temporal dynamics of building density in Colombo district using GIS techniques over a 50-year period (1975–2025). Building density was analyzed at 5-year intervals from 1975–2025 using secondary data. The collected data were standardized and analyzed using Buffer-based urban expansion, Pearson’s Correlation Coefficient, and Clark’s Negative Exponential Model. The results show that rural areas in Colombo district decreased rapidly (r=-0.992), while peri-urban (r=0.959), urban (r=0.979), and dense urban areas (r=0.937) expanded. In 1975, the Colombo district was predominantly rural, showed urbanization moving from coastal area toward suburban zones. High-density development expanded eastward from the central business district by 2025. Although building density increased over time in the study area, the overall pattern of urban growth remained predominantly characterized by horizontal spatial expansion. The urban density gradient declined from 0.18 in 1975 to 0.08 in 2025. From 1975 to 2000, the central business core strengthened (7286.29 to 8701.98 per m2), while after 2000, it stabilized. Proper placement of buildings within urban areas, along with sustainable planning and technological approaches, supports effective management of urban zones.