Humanifica's understanding of geographic objects is a complex process, it needs to abstract a series of specific objects to abstract information we can expressed on your computer. The geographic space information is in fact it is everything we got to browse the map, and its main purpose is to tell people "What is anywhere", and the digital geospatial information is the computer coding and display mode on geospatial phenomena. Representation. However, because the map is our simple abstraction of the Earth entity, we can think of the Earth image is a map, or the collection of unpleasant earth phenomena collected with any simple instrument is considered a map, which is different. The difference between the human phenomenon, the difference, etc., the difference is obvious [Raafat H, et al., 1994]. This is the case for digital information. With different data structures, storage methods, analysis models, etc., there is a chaos in the field of digital geographic space information, which has brought great inconvenience to the sharing of information. In order to promote the sharing of geographic information, there is an overall understanding of the entire cognitive process of geographic information, ie the relationship between geographic elements should be more clear. The element here refers to the basic unit of geographic spatial information. It can gradually consist of complex elements, such as a satellite image, one pixel in the image, a non-regular triangular network, superimposed on the weather map. Temperature, etc. The abstract process of geographic objects is usually considered nine hierarchies, and connects to them through eight interfaces between nine hierarchies to achieve conversion from the real world to geographic elements. These nine hierarchicals are in the real world, concept world, geospatial world, scale world, project world, point world, geometric world, geographical elements, and elements collection world. Connecting their eight interfaces are known interface, GIS discipline interface, local geometry interface, group interface, spatial reference system interface, geometric interface, element structure interface, and project structure interface. Excerpted from http://gis.pku.edu.cn/resources/tr/interoperability/gis metadata.htm#_toc22991006
