"Concept maps are graphical tools for organizing and representing knowledge. ...Propositions contain two or more concepts connected using linking words or phrases to form a meaningful statement. Sometimes these are called semantic units, or units of meaning. ...[C]oncepts are represented in a hierarchical fashion with the most inclusive, most general concepts at the top of the map and the more specific, less general concepts arranged hierarchically below. ...[I]t is best to construct concept maps with reference to some particular... focus question. ...Cross-links help us see how a concept in one domain... on the map is related to a concept in another domain... on the map. In the creation of new knowledge, cross-links often represent creative leaps [by] the knowledge producer. ...[S]pecific examples of events or objects... help to clarify the meaning of a given concept. ...Concept maps were developed in 1972 in the course of Novak’s research program... to follow and understand changes in children’s knowledge of science... [T]he researchers... found it difficult to identify specific changes in the children’s understanding... by examination of interview transcripts. ...Out of the necessity to find a better way to represent children’s conceptual understanding emerged the idea of representing children’s knowledge in the form of a concept map."