Several combined link and slide devices have been described, by means of which block diagrams can be constructed from contoured maps (1, 2). Briefly, their mode of use is as follows: (a) On tracing a contour with the tracing point of the mechanical device, the drawing pencil reproduces the contour as its isometric projection, i.e. distances along the supposed line of sight are reduced relative to distances measured at right-angles to this direction, the reduction factor being determined by the angle at which the area is assumed to be viewed. (b) Before drawing the isometric projection of the next lower contour, the sheet of paper on which the diagram is being made is moved relative to the map in a direction depend-ing on the type of device by a distance which depends on the scale of the map, the contour interval, the angle at which the area is viewed, and any factor of vertical scale magnification relative to the horizontal scale which is deemed necessary to bring out the topography (2). Each successive contour is treated in this manner, preferably starting with the highest contour and finishing with the lowest. In drawing the isometric projections of the contours, such parts are omitted as their inter-sections with the higher contour projections show to be obscured by the intervention of high topography between them and the point from which the area is viewed. (c) Finally hill sky-lines are filled in, roads, rivers, etc, are drawn by sketching between the points where they have been marked as crossing contours in dealing with each contour, and such artistic additions are made as will enhance the impression of relief.