Spatial Thinking in Planning Practice: An Introduction to GIS

14 Figure 2.3. "e concept of Map Projection as illustrated using a spherical globe and a 'at map. http:// 2012books.lardbucket.org/books/geographic-information-system-basics/s06-02-map-scale-coordinate-sys- tems-a.html Within the realm of maps and mapping, there are three surfaces used for map projections (i.e., surfaces on which we project the shadows of the graticule). "ese surfaces are the plane, the cylinder, and the cone (Figure 2.4). Figure 2.4. "ree types of “'attenable” surfaces to which the graticule can be projected: a plane, a cone, and a cylinder. https://www.e-education.psu.edu/geog482fall2/c2_p30.html As you might imagine, the appearance of the projected grid will change quite a lot depending on the type of sur- face it is projected onto, and how that surface is aligned with the globe. "e three surfaces shown above in Figure 2.4 -- the disk-shaped plane, the cone, and the cylinder--represent categories that account for the majority of projection equations that are encoded in GIS so$ware. "e plane o$en is centered upon a pole. "e cone is typi- cally aligned with the globe such that its line of contact (tangency) coincides with a parallel in the mid-latitudes. And the cylinder is frequently positioned tangent to the equator (Figure 2.5). Chapter 2: Coordinate Systems and Projecting GIS Data