Guide: This chapter describes the core content of the whole GIS theory. In order to use information system tools to describe the real world and solve its problems, it is necessary to model the real world. For Geographic Information Systems, the result is a spatial data model. Spatial data models can be divided into three types：
Field model: It is used to describe the phenomenon of continuous distribution in space；
Element model: It is used to describe various spatial objects；
Network model: It can simulate all kinds of networks in the real world；
Among these models, some related concepts are introduced, such as spatial partition, spatial relations, and the formal description of topological relations - 9 intersection model.
Finally, it describes the expansion of general two-dimensional data model in space and time, time data model and three-dimensional data model.
It is worth noting that the field model and element model mentioned in this chapter are similar to the latter mentioned raster data and vector data, but the former is a conceptual model, the latter refers to its implementation in information systems.
