The central and historical textures of cities have always been considered primary manifestations of a city's history and identity. In recent decades, such textures have received growing attention from urban designers and policymakers through infill development. This study aims to model and design infill development based on urban design and policy-making approaches. The design approach includes four dimensions: objective aesthetics, mental-cognitive aesthetics, functional, and environmental aesthetics. The policy-making method comprises three dimensions: social capital, economic infrastructure, and assessing the situation of the local area. In this study, a mixed-method approach was used to measure and analyze quantitative and qualitative data. Data collection was conducted through interviews with experts in management, planning, and urban design. The discourse analysis technique was employed to refine the data obtained from the interviews and to complete the proposed models. Subsequently, the collected and refined criteria were analyzed based on the opinions of experts using MAXQDA software. The obtained model was then analyzed using MicMac software, considering experts' opinions to understand how the components affect each other, presented in the form of charts and analytical graphs. In the final step, approaches, dimensions, components, and indicators were modeled based on the importance of the components using Sankymatic software. The findings aim to present a practical model for infill development in the central and historical areas of Mashhad, as well as valuable textures of urban hubs, especially in the metropolises of Iran. Analyzing selected components in the modeling of infill development helps to provide effective strategies for valuable and central textures of cities that embody an urban identity. This study, in terms of urban planning (policy-making) and urban design (designing), presents reviews and analyses across different dimensions. Providing a comprehensive and efficient model with proposed solutions tailored to each component with the infill approach is considered a desirable method for developing valuable central and historical textures, particularly in metropolises. To date, no comprehensive model has been presented to explain the indicators of infill development from the perspectives of urban design and urban planning. This study articulates the approaches, dimensions, components, indicators, and corresponding proposed solutions in the form of a research model.
