Nature Notes

Vol. XIII June - 1935 No. 2

How To Make A Relief Model

One of the major features of interest in the Park Museum at Longmire and in the Community Building at Paradise is the large relief model of this park which is on display at each of those places. Both of these models are identical, having been cast from the same mold. Because they are accurate and faithful to detail, the park visitor is thus able to view "The Mountain" in much the same manner as if he were flying over the actual park in an airplane. This interest has resulted in many questions regarding the manner of preparing such a model. The great majority of these questions are prompted by more than idle curiosity, and we take this opportunity to outline, in general, the steps in the process.

Building a relief model requires considerable hard work, careful application to detail, a lot of patience and a lot of time. Anyone contemplating such a project should first resign himself to those facts, otherwise the completed model - if it ever is completed - will not be satisfactory. The character of the completed model will also be largely determined by careful planning of all details (size, horizontal scale, vertical scale, etc.) before a bit of material is purchased or a start on the actual work is made. And now for the outline of the process.

(1) A good topographic map of the region to be modeled is, of course, necessary. This map serves as the pattern. The numerous wavy lines give us a picture of the region's topography. Each wavy line (contour line) connects points of equal elevation. Where these lines are far apart a gradual slope is indicated; where they are close together a steep slope would be found. (Fig. A and Fig. B illustrate the principle of the topographic or contour map - a small hill serving as an example. In Fig. A. the contours, connecting points of equal elevation on this hill, are shown. The vertical distance between them is 100 ft. and this is known as the contour interval. There is a gradual slope on the left and a steeper slope on the right. In Fig. B. we see a cross section of this hill with dotted lines indicating the position of the contours on the mapped area of Fig. A.)

Figure A: topo map, Figure B: cross section map

(2) The foundation of the model is built up of layers of cardboard. The thickness of each cardboard layer indicates the contour interval of the map - a layer, in miniature, of the earth. The wavy pattern of each contour is first traced upon a sheet of cardboard, then cut out. In order to simplify this description we will assume that the model to be made is to be of the same size as the map. (If it is desired to enlarge the model, lantern slides of the map are first made. These lantern slides are projected upon a wall, by means of a sterioptican, to the desired size and the contours traced, as described below, from the projected image.)

As each is traced and cut it is placed upon those that have gone before and tacked or glued down until the foundation is completed. It will then have the appearance of an oriental terraced farm. Because each thickness of cardboard indicates the map's contour interval the vertical scale of the model must be given careful consideration for it determines the thickness of the cardboard that will be used. If the cardboard is too thick the hills will be too high and the valleys too narrow and if it is too thin the reverse will be true. One may compute the thickness of the cardboard necessary by dividing the horizontal scale of the map by its contour interval. (If one inch equals 1000 feet on your map and the contour interval is 25 ft. the cardboard to be used should be one fortieth of an inch thick. If the contour interval is 50 ft. the thickness of cardboard should be one twentieth of an inch, etc.) By computing the vertical scale in this manner we will build a model in which the horizontal and vertical scale are the same - the topography of the model will be an exact miniature of the actual area. However many relief models have the vertical scale exaggerated. This is particularly true of those dealing with comparative flat regions where topographic differences are not of an abrupt enough character to make them stand out in the model. Exaggeration in such a case may be justified for then the hills and valleys of the model appear to the eye more nearly as they actually seem to us as we view them from the ground level. For areas of rugged topography it is not necessary to exaggerate the vertical scale and the tendency today in the building of such models is to make the vertical and horizontal scale the same.

(3) In starting the foundation first locate on the map the contour of lowest elevation. This should be traced upon the first sheet of cardboard and the resulting pattern cut out and placed upon a suitable base which has already been provided. The first cut-out will usually be the outline of the map with a small notch, or notches, along the edge. (In Fig. C. the shaded portion indicates the base of the foundation and the heavy line a portion of the lowest contour which had been traced, cut out and glued or tacked to the base. The dotted line is a portion of the next highest contour which has been sketched in to serve as a guide in placing the next thickness of cardboard. Fig. D. is a side view of the same except that the second and third thicknesses of cardboard have been laid on. The legend in each case is the same.) As each contour is traced it is well to trace the next highest one to serve as a guide in placing the next cardboard layer. Cutting is done with a jig-saw, cut-awl or some similar instrument capable of doing accurate work. As each contour is traced, cut and tacked down, the foundation will gradually take form. The large cut outs break up into smaller units and individual hills and valleys appear. When the foundation is completed it will be composed of cardboard terraces which are in reality the contour intervals of the earth, as indicated by the map, in miniature and to scale.

Figure C: level of 100 ft. contour, Figure D: 100/200/300 ft. contour

(4) Upon this foundation plastic clay is worked into the terraces until the step-like effect is obliterated. This should be done very carefully; applied just thick enough to cover the edges of the layers (See Fig. E. and Fig. F.). Work in all topographical details with the fingers and with modeling tools until the model is as finished and faithful a presentation of the area as it is possible to be. When this is done you are ready for casting.

(5) We first cast the "negative" - a replica of the model upside down. Before casting the model experiment with plaster of paris by casting small objects such as irregular gobs of plastic clay, etc., until you get the "feel" of how plaster of paris works. The clay model is now greased or soaped (lather it as in shaving) to prevent the plaster from sticking to it and sides are built up to prevent the plaster from running beyond the models bounds. A large bucket of plaster is mixed until it has a "soupy"" consistency. Ladel this "soup" on the model until a thin layer covers it entirely. Now quickly dip strips and squares of burlap (provided before hand and made ready to use) into the plaster and lay them, dripping, upon the model. They will merge with the thin layer of plaster which was ladeled on and, as they are placed so that they overlap, will give strength to the cast when hard. Another layer of plaster is laid on and another layer of plaster-soaked burlap follows. (It may also be necessary to reinforce a large cast with wooden or metal rods set in the soft plaster before the last burlap layer) The plaster is now smoothed out and the entire cast allowed to set. When sufficiently hard the sides are taken away and it is gently worked at the edges with the fingers until the negative pulls away from the clay model. A little touching up may be necessary, then the negative is allowed to dry following which it is shellacked. We are now ready to cast the "positive" - an exact replica of the clay model.

Figure E: layers, Figure F: clay overlaying layers

(6) Casting the positive is quite similar to the method used in casting the negative. The negative cast is first greased to prevent sticking, the thin plaster is ladeled on followed by layers of plaster-soaked burlap until a shell of sufficient thickness is built up. It is then allowed to set and the two sections worked apart. Touching up follows and the positive is then shellacked and made ready for painting. If your negative was a good strong one, any number of positive casts may be made from it. Very large models are cast in sections (as in the case of the Mount Rainier National Park relief model) and fitted together like a jig-saw puzzle.

(7) Painting in the various colors to indicate barren rocky areas, timbered sections, roads, trails, etc., follows. When this is done the model is complete and is ready to be installed upon some suitable table or hung in a suitable place on the wall.

C. Frank Brockman,
Park Naturalist.

<<< Previous
> Cover <
Next >>>