The Use of Deformational Data in Evaluating World Map Projections

T HE devising of new systems of map projection apparently holds a fascination quite out of proportion to other projection problems. Particularly does this seem to be true when one considers the modern literature concerned with the choice and the evaluation of map projections; with only a few notable exceptions, there seems to be comparatively little cartographic research aimed at the better selection of projections. Yet the modern cartographer appears reasonably assured of a constant supply of new projections. The problem of choosing a projection is, however, the major portion of the cartographer's concern with projection. Without intent to depreciate in any way developments in an interesting field, this author cannot help but conclude that the need for new projections is far overshadowed by the need for a rational basis for evaluating and choosing from the projections now available. Except when the proposed map clearly dictates a specific projection for a specific use, e.g. Lambert or Mercator for navigation, it may be stated as a general rule that the importance of proper selection varies directly with the size of the area to be presented. Hence the most difficult and important selection is choosing a projection on which to present the whole earth. Once the primary purpose of a map has been established, e.g. distribution, as well as the projection property necessary (equivalence), the cartographer still has considerable choosing to do. To illustrate his very real dilemma, there are at least, a half dozen conventional, easily constructed, equivalent world projections. There actually is no limit to the number of possibilities. Most of them can easily be made into oblique* phases. The majority, probably, lend themselves to interruption. And, more important, the land areas may be plotted in an infinite number of ways depending upon the one or several central meridians chosen. Clearly the cartographer needs some basis for evaluation and selection from this truly imposing array of possibilities. The most useful basis would, of course, be some sort of composite diagnosis of the purposes of the map, which would have as a corollary a prescription of the solution. Such is clearly not possible. The cartographer, lacking such a nostrum, can only proceed to narrow the field as far as possible with the aid of measurable characteristics and then make his choice from the remaining alternatives. The projection requirements of every map are theoretically different. The proposed map may dictate straight parallels, or straight meridians, or both; it may require equivalence, or azimuthality, or some other property. Yet when the cartographer has threaded his way through the list and has eliminated all the inappropriate projections, he must still choose from a large number of possibilities. Both the