Lab 5

Understanding map projections is important when you are trying to find locations or measure or plan any sort of route or path. Every map made requires some sort of distortion of Earth's true dimensions, and so knowing which map (and form of distortion) to choose is vital in order to be as accurate and precise as possible. When navigating, for instance, conformal maps are most helpful as they preserve shapes at local levels and line angles throughout. When comparing geographic distributions, we would want to use an equal-area map which will allow us to compare area. If we wish to derive distances from a central point, an equidistant map would be our best choice. Note, however, that each of these maps has its downfalls and none is well fit for anothers primary use.

Conformal maps preserve local shapes while allowing for a relatively straightforward navigation. Meridians and parallels intersect at right angles, which provides us the ability to align our compasses with the squared latitude and longitude directions. The Mercator projection is widely used as world map as it represents Earth as a simplified squared North-East-South-West grid. Because of the usefulness of this projection when navigating, most map-based web services (google maps, bing.com, etc) use some form of web-adapted Mercator maps, as shown to the right in figure 1. However, these maps are not useful when comparing area. Because of the way in which the spherical meridians are manipulated to create right angles upon a cylindrical plane, area is greatly exaggerated towards the poles. At a local scale, however, this gradual stretching of area does little to manipulate human-scaled shapes, such as buildings and streets, and so also remain useful for simple, localized referential navigation. Buildings retain their true shapes, as do local regions and other objects on large-scale maps.

Equal-Area preserves an area on a map. In these maps, each quadrilateral formed by two parallels and two meridians on the map represents the same amount of area on the globe. These maps are useful when comparing geographic distributions because area is represented truly. It is important to employ these maps when trying to represent any sort of geographic distributions, whether of land or other phenomena such as resources and population, because otherwise observers might be led to see the world wrongly, a misfortune that may influence their perception of the world for years after. For example, when we compare our Mercator maps to our equal-area projections, we can clearly see the flaws in the conformal maps. The difference in size between Greenland and Africa is represented truly in our equal area maps, yet in the Mercator maps Greenland is projected and appears to challenge Africa in size. In reality, Greenland is small, closer to the size of Mexico than Africa.

Equidistant maps show you the true distances from the center of the projection. The good thing about this is that if you can find a map centered on your city of choice, distance is preserved going outwards from that point in any direction. That is, any line spanning from the center to point A on the map will cover the same distance on the earth if we were to take that line to connect the center with another point of equal distance away from the center on the map as point A. This is useful when working with specific cities, but proves problematic when trying to measure distances between two points on the map which are not the center. If a map is centered on Atlanta, for instance, and represents the whole of the United States, the measurement of distance from Atlanta to New York would be true to the distance on the globe. However, if we were to measure the distance on the map between New York and Los Angeles we would not attain a true measurement of the distance between these cities on the globe.

Each map projection has its strengths and weaknesses, and we must understand these in order to decide which projection is the best fit for our purposes. Luckily, GIS software allows us to easily switch between different projections using the same true sphere-based data. We can easily switch between a conformal map to an equal area map and so easily observe and measure the differences in representation. While the different projections within each type of projection still puzzle me, the understanding I am gaining by working with ArcMap is invaluable as far as better utilizing my data through different maps. Each projection is a different tool in our hands to better represent what we are trying to show with our data.