Modelling is central to many disciplines in engineering and the natural and social sciences. A wide variety of modelling languages and tools have been proposed along the years, traditionally for static environments such as desktops and laptops. However, the availability of increasingly powerful mobile devices makes it possible to profit from their embedded sensors and components (e.g. camera, microphone, GPS, accelerometer, gyroscope) for modelling. This has promoted a new range of modelling tools specially designed for their use in mobility. Such tools open the door to modelling in dynamic scenarios that go beyond the capabilities of traditional desktop tools. For example, modelling in mobility can be useful to design smart factories on-site, or to create models of hiking routes while walking along the routes, among many other scenarios. In this paper, we report on a systematic mapping study to identify the state of the art and trends in modelling on mobile devices. The study covers both research papers and modelling apps from the Android and iOS stores. From this analysis, we derive a classification for mobile modelling tools along three orthogonal dimensions, discuss current gaps, and propose avenues for further research.