Hi, and welcome to this video on map projections! Today, we’ll look at several different map projections and see how each of them portrays the earth a bit differently than the others.
When creating the maps that guide travel, economy, and our society every day, cartographers face the problem of depicting true proportionality while maintaining usability. To explain further, the object in question is the spherical Earth and the two dimensional medium is often a flat display. Knowing that the earth is spherical helps to bring the problem into context: if you hold up a ball, you cannot view the opposite side at the same time as the one you are looking at without a mirror or another device. Any globe will more accurately represent specific size and location when comparing different areas of the planet as it mimics the true physical shape of the Earth, but they are not always practical to carry around or quickly consult when detail is required. To view the entirety of the planet at the same time on a flat surface, a map projection is used. Simply put, a map projection is the descriptive term explaining the way in which longitude and latitude of the earth are distorted to accurately create a flat map. To note, the properties of area, distance, and form are mutually exclusive. If you have a map projection that preserves one, it will distort the other two.
There are several general classifications of map projections, each with their own list of subtypes. To simplify things, we will focus on 5 specific classifications: Conformal, Equal-area, Equidistant, Gnomonic, and Retroazimuthal.
In cartography, a conformal map projection, like the Mercator projection seen here, is one in which every angle between two curves that cross each other on Earth are preserved in the image of the projection. This allows for the shape of features to be preserved at the cost of their size/area.
Because of this, conformal projections preserve only smaller ratios while inherently distorting larger figures. Notice how Greenland appears to be the same size as Africa, when, in reality, Africa is 14 times larger than Greenland. In a conformal projection, parallels and meridians cross rectangularly on the map, but do not preserve other angles.
The equal area projection retains the relative size of area throughout a map, keeping the true size of features, such as oceans and mountain ranges. While this type of projection preserves area accurately, it tends to distort shapes and angles, which means it CANNOT be conformal. Equal area map projections are useful for comparing broad areas but are difficult to use for navigation.
Equidistant maps show true distances only from the center of the projection or along a special set of lines. For example, an Azimuthal Equidistant map centered at the North Pole shows the correct distance between the North Pole and any other point on the projection. It shows the correct distance between the Pole and Copenhagen, and the Pole and Seattle. But it does not show the correct distance between Copenhagen and Seattle. It should be noted that no flat map can be both equidistant and equal area1. Equidistant maps are useful for things such as determining the direction to aim your antenna when utilizing terrestrial point to point communication.
Gnomonic map projections, also known as azimuthal gnomonic map projections, display all great circles as straight lines, resulting in any straight line segment showing the shortest route between the segment’s two endpoints. This is achieved by projecting points on the surface of the sphere from the center to a point in a plane. From this tangent point, less than half of a sphere is visible, with the projection remaining undistorted at the central point and becoming increasingly distorted as you move away from it towards the edge of the map.
Gnomonic maps are used when tracking the paths of seismic waves and determining paths of travel for boats and airplanes as they accurately describe the shortest routes across the planet. To explain further, straight geodesic line segments on a non-gnomonic map would appear curved, leading to the common name “great circles”. When viewed from above the North or South Poles, these lines appear as concentric circles expanding from the center of the map projection. This occurs because the same distortions used to convert a globe into a flat image also visually curve the geodesic lines.
To understand retroazimuthal map projections, it is important to understand why they are some of the most greatly distorted projections still utilized by people in our modern world. The purpose of a retroazimuthal map projection is to show the most direct route from anywhere on the planet to a specific point of interest. Logically this makes sense, but visually it creates a challenge which has been handled in several different ways depending on the point of interest, the most notable of which being the Craig retroazimuthal projection, named after James Ireland Craig. This is also sometimes known as the Mecca projection because Craig, who had worked in Egypt as a cartographer, created it to help Muslims find their qibla. In such maps, Mecca is the configurable location of interest, with horizontal and vertical meridians allowing viewers to accurately face the center regardless of location on the planet.
Now, as you might have guessed, accidental or intended cartographic manipulation may take place during the process of mapmaking. When utilized correctly, this manipulation can result in the map highlighting certain elements or features in order to more accurately portray the desired information. An example of this occurring is apparent when considering physical maps against political ones. Most political maps focus on names of places and the borders between them, defining who controls what place, whereas physical maps focus on the topography of the area and what it physically looks like, including mountains, valleys, and rivers. Accidental manipulation occurs in such things as creating a map that is centered on one region, or containing more detail. When purposefully taken to an extreme, this practice is known as cartographic aggression.
Cartographic aggression is when a country produces maps that allegedly misrepresent the borders with a neighboring country. This has existed for millennia, with a more modern example seen in the depictions of the border between India and China on their respective maps. As there is technically no agreed-upon boundary, each country creates maps with borders that overlap in several different places. The conflicts that arise from such disagreements range from economic to political and occasionally armed military activity.
Thanks for watching, and happy studying!