Abstract

Map Projections Short Course
Track: Training
Authors: Craig Rollins

Map projections continue to be an important part of cartography, surveying, and GIS technology. Among the reasons for this are that (i) data display is still heavily 2D and printed maps are far from obsolete, (ii) data collection is often 2D as in the focal plane of cameras, and (iii) the design and understanding of national grids and the universal grids (UTM, UPS, MGRS) depend on the theory of map projections.

This one-day course examines the constructive principles and major properties of the most important map projections in a way mainly aimed at the needs of cartographers, surveyors, and GIS practitioners with some tips and equations briefly offered for the student of the theory. The discussion begins with an argument that a true-scale-everywhere map is impossible. This opens the door to the excitement of the subject and the plethora of map projections. The zoo is tamed by two classification schemes which are explained - (i) the classifications cylindrical, pseudo-cylindrical, conic, pseudo-conic, polyconic, and polar-azimuthal, and (ii) the classifications conformal, equal-area, and "equidistant". A matrix of the two classification schemes reveals the uniqueness of some well known map projections and the competition for superiority among others.

The emphasis is on the ellipsoid form of various map projections, making mere mention of those forms that pertain only to the sphere due to its greater symmetry. The emphasis is further placed on the conformal map projections and their properties, as they are the basis for world's grid systems. The map projection parameters for the Mercator, Polar Stereographic, Lambert Conformal Conic, and Transverse Mercator projections are examined in some detail, and their effects on the shape, size, orientation, and position of everything portrayed is explained. Two functions attend every conformal map projection, namely point-scale and convergence-of-meridians, and the importance and usage of these tools are explained. The specifications and properties of UTM, UPS, and SPC's are presented as particularizations of the above general ideas.

Throughout the day long course are interspersed several side-bars on the subject of scale, so that its various related concepts can be untangled.