In the field of geographical and environmental education, maps and geo-referenced information are frequently used, in which the earth's surfaces are represented in a two-dimensional (2D) way. Students have difficulty interpreting the relief representation and switching between 2D and 3D scenarios. Digital terrain modelling is added to the traditional cartographic techniques to represent the landforms, and the AR technology provides a new 3D and mapping human-machine interaction. In the 2015-2016 course, an educational experiment using AR on a tablet with 63 students from La Laguna University was performed covering three steps: academic improvement, usability of this technology to interpret the relief, and if it is motivating for the students. This paper presents the results in usability and motivation. A usability study in terms of efficiency, efficacy and satisfaction is presented. To assess student motivation, the Intrinsic Motivation Inventory motivational model with six dimensions is adopted. Results about AR on tablets in the interpretation of terrain relief show a great usability of this technology, which serves as a motivational tool for the 3D visualization.