Page:The National geographic magazine, volume 1.djvu/311

 of hachures may be roughly characterized as a graphic system with a conventional element, and the contour method as a conventional system with a graphic element,—for if the contour interval is small enough a sort of shading is produced which helps considerably the idea of relief.

In addition to these two great systems, with which everyone is more or less familiar, there is another method of representing a country or district,—a method that succeeds where others fail, and which although by no means new, has not received the attention it deserves: this is the representation of a country by a model in relief. Certain striking advantages of models over maps of all kinds are, indeed, so apparent that one almost loses sight of such slight disadvantages as can, of course, be urged against them. In the graphic representation of the surface they are far superior to the hachured map, and they have the further advantage of expressing the relative relief, which the hachured map fails to do, except in a very general way. They have also the advantage of showing actual shadows, exactly as they would be seen in a bird's-eye view of the district, instead of more or less conventional ones, and are, consequently, more easily comprehended by the layman, without becoming any less valuable to the skilled topographer. In short, they combine all the graphic features of a hachured map with all the advantages of the best class of contoured maps, and in addition they show more of the surface detail, upon which so much of the character of the country depends and which is very inadequately expressed by hachures and almost completely ignored in a contoured map of large interval. The contours themselves can be made to appear upon the model very easily and without interfering with other features.

The uses of models are many and various. Within the past few years their usefulness has been much extended, and, now that they are becoming better known, will probably receive a still further extension. To the geologist they are often of great value in working out the structure of complicated districts, for the reason that so many important structural relations can be presented to the eye at a single glance. Similarly, for the graphic presentation of results there is no better method, as the topography, the surface geology, and any number of sections can be shown together and seen in their proper relationship. To the engineer an accurate model is often of the greatest assistance