As a new field of visualization, knowledge visualization is to use maps, graphics, or images to construct and transfer insights and knowledge between at least two persons. In view of geovisualization, geographic diagram, geo-informatic Tupu, and visual analytics are cutting edge researches on visual and graphic representation and discovery of geographic knowledge. Thus, this paper focuses on the discussing of geographic knowledge visualization in terms of general knowledge visualization and geographic diagram. In the paper, the concept and characteristics of knowledge maps in geographic knowledge visualization are mainly explored according to the dual coding theory of representation of mental images, features of geospatial thinking, and need for supporting visual exploring of geo-knowledge.

Geo-knowledge maps are defined as cognitive and abstract maps involved in geo-problems, geographic spatiotemporal distribution, relationship of geographic factors, and so on. They should be fit for mental image representation and cognitive process, and benefit human spatial memory, thinking and imagination to improve capability to handle geo-problems. Considering images like digital camera photos and remotely sensing images, they all mimic the physical world in real life without any abstracting and any adding of human thinking and reasoning. Therefore, this paper defines these mimic images as geo-information images which have differences from geo-knowledge maps that express human knowledge about the real world. Because of the relative differences between geo-information images and geo-knowledge maps, geo-knowledge maps have two kinds: weak and strong. Weak geo-knowledge maps refer to that there are more objective, concrete, and mimic description, while strong maps have more subjective involvement and more abstracting.      

Geo-knowledge maps have two kinds of classes: concept propositional maps and analogue diagrammatic maps. Concept propositional maps highlight verbal handling of geographic phenomena, while analogue diagrammatic maps do non-verbal handling，i.e. representation of geographic graphics and images. With regard to analogue diagrammatic maps, there are further four types: logic and topological similar maps, spatial structure similar maps, variable-relationship similar maps, and process similar maps. As a case study, a few of practical knowledge maps for supporting spatial planning of dam systems in watersheds are presented.

Keywords: Knowledge visualization, knowledge map, diagram, geographic cognition, spatial planning of dam systems, virtual geographic environments

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