Raised-line diagrams are widely used by visually impaired (VI) people to read maps, drawings or graphs. While previous work has identified general exploration strategies for raised-line drawings, we have limited knowledge on how this exploration is performed in detail and how it extends to other types of diagrams such as maps or graphs, frequently used in specialized schools. Such information can be crucial for the design of accessible interfaces on touchscreens. We conducted a study in which participants were asked to explore five types of raised-line diagrams (common drawings, perspective drawings, mathematical graphs, neighborhood maps, and geographical maps) while tracking both hands fingers. Relying on a first set of results, we proposed a set of design guidelines for touch interfaces.