(Essay) An Explanation of Cylindrical Map Projections – Brandon Skenandore
Total word count: 756
Time spent researching and writing: 4 hrs
Cylindrical map projections are a type of global map. A cylindrical projection, according to Arthur H. Robinson, in his book Elements of Cartography, is when a map is projected by “first transforming the spherical surface to a tangent or secant cylinder. In all cases the lines of equal distortion are straight lines parallel to the standard lines” (71). This book also explains that “distortion will increase away from the standard lines, and the greatest gradient will be in the directions normal (at right angles) to the standard line” (72). Therefore, the most distortion will occur near the top and bottom poles of the globe since, as a sphere, the longitude lines are spread apart so that they are straight, not curved into one another near the top and bottom. Some types of cylindrical projections try to make up for this, however. Overall, a cylindrical map was and still is best used for navigation because these projections usually help point true north and south at all times.
One example of a cylindrical projection would be the Mercator projection. In our textbook, Geography for Dummies, Charles A. Heatwole explains that a Mercator projection is the most famous world map of all time. “Straight lines on this map correspond to true compass bearings so a navigator could use it to plot an accurate course” (53).
Indeed, this map has been used by navigators for a long time because the longitude lines point North, which helps when using a compass (See figure 1). However, Heatwole further explains that the projection is “extremely distorted with respect to size” (53). As you can see from the diagram, the Northern and Southern areas of the projection are very bloated, making Antartica look much bigger in proportion to the other continents. However, the latitude lines on the map attempt to account for the distortion that has taken place vertically. On the other hand, there is still distortion in respect to the spacing of the longitude lines, because they remain equidistant throughout the map.
Another good example of a cylindrical projection would be the Goode’s Interrupted Homolosine projection. In this projection, Dr. Paul Goode attempted to create a projection of equal area, so that the different continents would appear equal relative to each other (Heatwole 54). According to John P. Snyder, in his book Flattening The Earth, this map is interrupted in attempt to “reduce scale and shape distortion by choosing several central meridians to coincide with larger land (or ocean) masses, and constructing the projection in the regular manner to the east and west of each of these meridians until a particular landmass had been included” (166).
In essence, this map, while keeping area equivalent between all continents, maintains all continents intact, except for areas like Greenland and Antartica (See Figure 2). However, this type of map fails to aid navigation at sea because of the interrupted areas between the different Continents. While this map may try to minimize the inaccuracy, it does so not allowing for navigation to be very easy.
The final example of a cylindrical projection would be the Robinson projection. This projection, according to Mark Monmonier in his book Mapping it Out: Expository Cartography for the Humanities and Social Sciences, was adopted by the National Geographic Society in 1988 because it makes for a great reference world map for general purposes (38).
As you can see from the diagram, the longitude lines on this map come closer together towards the top and bottom of the map, attempting to account for the distorted area like the Mercator projection caused (See Figure 3). However, “Straight-line parallels that are evenly spaced…still distort area near poles” (Monmonier 38). Greenland and Antartica are still larger than they should be, but nowhere near as distorted as in the Mercator projection. This map, while still being somewhat troublesome for navigation, is used mainly as a reference to see more accurately the sizes of continents and how they relate to each other.
Heatwole, Charles A. Geography for Dummies. New York: Wiley, 2002. Print.Top of Form
Monmonier, Mark S. Mapping It Out: Expository Cartography for the Humanities and Social Sciences. Chicago: University of Chicago Press, 1993. Print.Bottom of Form
Robinson, Arthur H et. al. Elements of Cartography. New York: Wiley, 1995. Print
Snyder, John P. Flattening the Earth: Two Thousand Years of Map Projections. Chicago: University of Chicago Press, 1993. Print.