Lab 5: Projections in ArcGIS

Map projection is about taking the globe, a 3 dimensional object and converting it into the 2 dimensional world. However when making these conversions, distortions are inevitable. There are three broad categories of map type to choose from, Equidistant (preserves distance from some standard point or line), Equal Area (preserves area) and conformal (preserves shape). There are many different types of map projections within each category, but the use of these maps depends entirely on the purpose. Each category has its disadvantages and no map is perfect.

As aforementioned, Equal area map projections preserve area and help retain the actual shape of area's on the earths surface relative to the map. I used the Hammer and Bonne (mistakenly labelled) projections to create these equal area maps. They are useful for studies that are attempting to represent the concentration of an attribute in an area - for example a dot density map. The Hammer map would be better at showing this than the Bonne map as this map is heart shaped and may not be as clear.

(Bonne Map (Bottom) mistakenly labelled 'Plante Carree'

On the other hand, Conformal map projections have all the lines of longitude and latitude lines intersecting at right angles and consequently do not retain area or distance. The examples I've used are the Mercator and the Stereographic projection. Both maps have huge distortions. With the mercator, you can see that as you move with latitude countries get larger – Greenland looks vastly bigger than its true size. The same can also be said with the Stereographic projection, which greatly reduces the size of Africa. Conformal maps, however are extremely important in complex analysis as well as in many areas of physics and engineering.

Finally, Equidistant map projections preserve the true distance from map to ground surface. The examples I've used are the Equidistant conic and Plate Carree. They again come with their disadvantages. As you can see, both over emphasise the area of land forms and distortions get more pronounced with latitude. However, equidistant maps are useful for navigational purposes.

Map projections are essential to our understanding of the world. The Mercator map is the dominant world map and previous to this lab I had not realised how large Africa was. Furthermore its clear that maps can also come with a political agenda as shown the with Cold war and the Soviet union – The USA wanted to over emphasise the size of Russia in order to portray a larger force than was actually there. This reaffirms my belief that understanding the basics of map projection is essential when deciding on which map projection to use for a piece of work or project.