The original idea of the principle of three-dimensional geographical time-space must be credited to Pr Philippe Mathis in his 1990 paper for the Association de Science Régionale de Langue Française (ASRDLF) workshop on distance and spatial analysis in Chamonix.
The document is a word-processor printed file but with freehand diagrams by Mathis and notably the key diagram of page 5 reproduced here.
On Mathis origin diagram fastest transport mode occupies the two dimensional usual plane, while slower edges of the transport graph are drawn above or under the surface as curves, proportionally longer than the Euclidean straight line. It is striking to observe that the most recent images of the model with cones and rounded edges are much more similar to this origin drawing than the first computer software implementation by L’Hostis in 1993 based on broken lines.
It is not surprising to know that Mathis has always conducted artistic activities beside and after his academic career with drawings, portraits, geometric drawings, and more recently sculptures.