The general objective of this study is to examine the socio - spatial development trajectory of the informal settlement Santa Rosa de Lima de Huancayo, Peru, over 40 years (1985 - 2025), focusing on unregulated urban development and infrastructure interventions. Adopting a longitudinal case study design with documentary analysis, systematic observation, and household interviews, this study explores four axes of development: social, economic, environmental, and urban - architectural. The analysis reveals extensive and largely unregulated urban expansion, marked by degradation of public open space, an increase in self - constructed residences, and a semi - structured urban landscape. This irregular pattern gradually develops partially structured streets and block configurations. A defining moment occurred with the 2011 opening of the Amazonas Bridge, enhancing connectivity and facilitating...