3-D multi-aspect mix degree index: A method for measuring land use mix at street block level

Land use mix refers to the integration of different land use types within a certain region, which is essential for sustainable cities. Comprehensive, accurate, and reasonable indices are priorities for evaluating the mixing degree, and current indices are mostly limited to two-dimensional (2-D) space. Based on three-dimensional (3-D) information from building and points of interest (POI) data, we improved the calculation methods of 2-D indicators and constructed a 3-D multi-aspect mix degree index, including single indicators (3-D diversity indicator, 3-D accessibility indicator and 3-D street block compatibility indicator) and a comprehensive indicator (3-D comprehensive mix degree indicator, CMDI3D). Considering the street block as study unit, results showed that Shenzhen had a high level of land use mix, especially urban centers with better socioeconomic conditions, and CMDI3D could delineate salient spatial heterogeneity. A comparative analysis revealed that CMDI3D was less affected by spatial scales, negatively correlated with travel distance (r ≤ −0.145), and strongly intercorrelated with other single indicators (r ≥ 0.40), which proved its stability and capacity to provide additional characteristics. Compared with 2-D Indicators, empirical verification and stronger correlations with travel distance also validated the effectiveness and advantages of 3-D Indicators. The proposed index can significantly help to improve urban planning and management.