“mental maps” in the sense that Geographers use it, is all about the drawing of maps by people who are not professional cartographers. The researcher asks surveyed individuals to actually draw on a piece of paper a sketch map of a given town or locality, noting significant places, landmarks, transport etc.
These are then analysed by “overlaying” them in some way, in order to pick out common features in the way in which the urban space is understood by its residents. The average map of different types of people can then be depicted (usually by a professional cartographer..)