I’ve found this site (LINK) with another explanation to the TAM model.
The map is a diagrammatic representation of the 28 core papers comprising the front in Economics & Business.
Each circle represents a highly cited paper whose bibliographic information is displayed when the user clicks on the circle. The lines between circles represent the strongest co-citation links for each paper (that is, indicating that the papers are frequently cited together). Papers close to each other on the map are generally more highly co-cited. The most recent paper(s) are indicated in pink. Annotations may have been added to this map which represent the main research themes. These appear as labels attached to specific regions on the maps.