Fig. 11From: A comprehensive bibliometric analysis of Catha edulis (Vahl) Endli (Khat) research (1961–2021)Overlay visualization map of author keywords with a minimum of five or more. There are 47 keywords on the map. The size of the node denotes an important issue and is proportional to the number of occurrences in the retrieved documents. The overlay visualizations in this figure show how these research topics have progressed over the course of timeBack to article page