Knowledge Engineering : Knowledge Management : Concept Maps

Concept maps are graphical tools for organizing and representing knowledge. They include concepts, usually enclosed in circles or boxes of some type, and relationships between concepts indicated by a connecting line linking two concepts.

A concept map or conceptual diagram is a diagram that depicts suggested relationships between concepts.

It is a graphical tool that instructional designers, engineers, technical writers, and others use to organize and structure knowledge.

A concept map typically represents ideas and information as boxes or circles, which it connects with labeled arrows in a downward-branching hierarchical structure. 

The relationship between concepts can be articulated in linking phrases such requires, or contributes to.

The technique for visualizing these relationships among different concepts is called concept mapping. 

Concept maps define the ontology of computer systems. We can easily say Concept maps can act as effective ways for Knowledge Representation.

There are some popular tools available for concept map drawing, you can refer to below link for more information about concept map drawing tools.

https://ltlatnd.wordpress.com/2011/05/11/ten-popular-concept-mapping-tools/

Following shows a sample concept map on FOOD, on how "Without the industrial chemical reduction of atmospheric nitrogen, starvation would be rampant in developing countries" :