We propose a new Geographic Information System (GIS) three-dimensional (3D) data model based on conformal geometric algebra (CGA). In this approach, geographic objects of different dimensions are mapped to the corresponding basic elements (blades) in Clifford algebra, and the expressions of multi-dimensional objects are unified without losing their geometric meaning. Geometric and topologic computations are also processed in a clear and coordinates-free way. Under the CGA framework, basic geometrics are constructed and expressed by the inner and outer operators. This expression combined geometrics of different dimensions and metric relations. We present the structure of the framework, data structure design, and the data storage, editing and updating mechanisms of the proposed 3D GIS data model. 3D GIS geometric and topological analyses are performed by CGA metric, geometric and topological operators using an object-oriented approach. Demonstrations with 3D residence district data suggest that our 3D data model expresses effectively geometric objects in different dimensions, which supports computation of both geometric and topological relations. The clear and effective expression and computation structure has the potential to support complex 3D GIS analysis, and spatio-temporal analysis.conformal geometric algebra, 3D data model, 3D measurement, 3D spatial relation Citation:With the development of GIS from 2D to 3D and temporal GIS, the 3D GIS data model is one of the most important current issues in GIS [1]. There is already a significant amount of literatures on 3D topological models [2-5], the expression framework of spatial relations [6-8], visualization mechanisms [9-14], integration of 3D GIS data [15][16][17] and spatial databases [18][19][20][21][22]. These 3D spatial data models have already been applied to various fields such as digital cities [23][24][25][26][27][28], digital oceans [29] and digital mines [30,31]. However, significant limitations in existing data models are present in the expression of geographical objects, relations building in multi-dimensional space, geographical analysis, and operations supporting geographical models in multidimensional space [1,32]. Constructing new types of 3D GIS spatial data model, which can support the expression and operation of unified multi-dimensional geographical objects, and supporting complex spatial analysis models and geographic analysis models, is the main direction of 3D GIS spatial data model research. This is needed to advance analysis in complex space.Most current data models are designed according to Euclidean geometric frameworks, and are limited by the difficulty and complexity of higher dimensions. The extension of 2D GIS to 3D GIS and temporal GIS also leads to problems such as spatial semantic ambiguity, information incompleteness in spatial queries, ambiguity and uncertainty of spatial characteristics, and increasing complexity of spatial modeling and reasoning [33,34]. Current 3D GIS requires more advanced computational operators that supp...