A Method for Measuring the Visual Coherence of Buildings in Residential Historic Areas: A Case Study of the Xiaoxihu Historic Area in Nanjing, China

Residential historic areas are currently the main focus of urban renewal efforts in China, primarily consisting of traditional residential buildings with similar characteristics. Hence, the visual coherence of buildings (VCoB) plays a crucial role in such areas, not only pertaining to the visual quality of the urban landscape but also regarding the preservation of historic features. The accurate measurement of the VCoB is a prerequisite for undertaking optimization efforts. However, discussions of the VCoB in the built environment are limited and seldom address residential historic areas, and methods for measuring the VCoB have yet to be refined. Therefore, taking the Xiaoxihu Historic Area in Nanjing as a case study, this work aimed to develop a more refined method for measuring the VCoB in residential historic areas based on objective physical features. The method is mainly based on the human-level perspective, identifying three key visual elements within this perspective as the objects of measurement. It collected visual data through photography, with deep learning and computer graphics processing tools being utilized to identify and extract the visual elements. Then, the study established a corresponding framework of indicators for different visual elements and optimizes the methods for indicator calculation. Through an assessment involving professionals, we validated the high accuracy of the measurement method proposed in this study. Furthermore, the study discusses factors affecting the VCoB, methods to enhance the VCoB, and the required degree of the VCoB based on the results of the measurement. The method developed in this research will provide support for the visual analysis of the urban built environment and urban renewal practices.