Projecting a 3D surface of the Earth on a 2D plane of a map is a hard task to accomplish. There is lots of work involved, and lots of calculations to perform, with the end result that’s more or less true to the original. Creating a map projection includes lots of mathematics, with some of the methods being graphically based but still requiring different calculations.
Basically, creating a map projection is a three-step task. Firstly, one must decide which model for the shape of the Earth will be used. There are two models, spherical and ellipsoidal, with the latter being closer to the actual shape of the Earth. After a decision has been made regarding the shape of the Earth, the coordinates must be transformed; geographical coordinates ((longitude and latitude) are transformed into plane coordinates (eastings and northings). Last, but not least, the scale of the map has to be reduced in order to accurately depict the area we want to show on a map.
After all this, the projection surface must be chosen. And since all maps use data originating from an ellipsoid body (the Earth), there are certain problems when trying to project an area onto a flat plane. You just can’t take a sphere or an ellipsoid and project it onto a flat, 2D plane. It would look like trying to make a flat surface out of an apple, or orange, peel. On the other side, we have surfaces that can be unfolded on a flat plane without distortion. Those surfaces are cone and a cylinder, and they can be used while making a map. Of course, the original projection of the Earth transformed into a cone or a cylinder will be distorted, but that’s a different problem.
The one property identical for all maps is the view of the map, which is always orthogonal (a straight down view). The orthogonal view is also called a normal view. And, while regular flat maps aren’t the best choice when it comes to the quality of the projection, they are the best choice since the globe, while being the perfect candidate for a map projection since it doesn’t distort any map property, isn’t so good when it comes to mobility, distance measuring, and the map view (when looking at a globe you can see only a small portion of the map).
When talking about different types of map projections it’s good to know that there are three most commonly used types of maps projections: Cylindrical map projections, Conic map projections, and Azimuthal map projections. Let’s present each of the three along with some of the most popular subtypes used.
Cylindrical Map Projections
As we mentioned already, a cylinder map projection can be unfolded on a flat surface (a map) without distortion, although the original Earth’s projection that’s pictured on the cylinder will be distorted. Cylindrical map projections are frequently used because they depict the surface of the Earth in an easy-to-understand manner.
All coordinate lines are flat out straight, and parallels are crossing meridians at right angles. All this makes the scale consistent across each parallel. Although this projection type is fairly easy to understand while looking at it, and while it is one relatively accurate depiction of the Earth, cylindrical projections are known for their severely distorted projections around the poles of the Earth. This is due to the fact that for making coordinates and parallels straight, the projection doesn’t take into account the natural curvature of the Earth. On the other hand, areas near the equator are presented with little distortion. This makes cylindrical projections great for making maps of an entire world but at the same time a poor choice when it comes to accuracy and true-to-life world visualization.
The most known types of cylindrical map projections are Mercator projection, Gall-Peters, Miller, and Cassini, among others.
Mercator projection is one of the best-known map projections of them all. It was created by Gerardus Mercator in 1569, and is characterized by a feature known as constant true direction. Constant true direction basically means that a straight line used for connecting any two points on the map is the same direction a common compass would show; really handy for the times it was constructed since back in the 16th century a compass was the most important piece of equipment of any explorer or a sailor. While the Mercator projection suffers from usual flaws tied to a cylindrical type of map projection, it is still widely used.
Robinson map projection
Another interesting type of cylindrical map projection is called Robinson map projection. Developed by Arthur H. Robinson in 1961 it takes the classic cylindrical formula and shakes it up a bit. For instance, the projection is curved and becomes more and more curved as the poles are closer. It depicts the Earth more accurately than a regular cylindrical projection, like Mercator, and it is so good that National Geographic use it for all of their maps ever since 1988.
Conic Map Projections
Conic map projections are defined by the cone constant, used for the angular distance between meridians. By using the cone constant, conic map projections feature equidistant meridians and parallels crossing the meridians at right angles. Another characterizing feature of all conic map projections is that they are constructed in a way that enables them to be wrapped around a cone on top of a sphere (the Earth). The line of latitude where the cone touches the Earth is called a Standard Parallel on all conic maps.
Conic projections aren’t really accurate, so they are not used for maps depicting the whole world. They are suitable for hemispheric maps and for maps depicting smaller regions. Some of the best known conic projection types are Lambert conformal conic, equidistant conic projection, and Albers conic.
Lambert Conformal Conic
Lambert Conformal Conic is the best known conic map projection type. It was constructed by Johann Heinrich Lambert, a German/French mathematician and scientist. He released his Conformal Conic projection back in 1772. His projection is characterized by having two standard parallels, and by having a conformal projection (meaning that shapes on the map are quite well preserved near the two Standard parallels).
Lambert Conformal Conic projection is popular for World Aeronautical maps, and from depicting large areas that are placed in middle latitudes (20° to 60° North and South) such as Australia, Europe or the USA. Lambert projection is rarely used for world maps due to the fact that it extremely distorts areas far away from standard parallels.
Azimuthal Map Projection
Azimuthal map projection is the third main type of map projections. It’s characterized by straight meridian lines (all meridian lines radiate from one central point), parallels that are circular around the central point, and equidistant parallel spacing. The azimuthal map projection is angular one. Given three points on a map – let’s call them A, B, nad C – are connected, and the azimuth from point B to point C is making the angle that someone looking at the map would have to look in order to get to the A point of the map. These relationships are known as geodesic arcs.
Azimuthal projection is based on a flat surface touching the Earth at one point. The distortions are increasing as they are more and more away from the central point, and they are very small near the center point where the flat surface is touching the Earth. They are commonly used for projecting the poles but are rarely used for areas near the Equator since other projection types better show areas near the Equator.
Universal Transverse Mercator System (UTM)
One special type of map projection is called Universal Transverse Mercator System (UTM). UTM was developed by NATO in 1947, dividing the Earth into a series of 6° of longitudinal wide zones, making a total of 60 longitudinal zones, each numbered from 1 to 60. These main longitudinal zones stretch from the North Pole to the South Pole, with a central meridian placed in the middle of each longitudinal zone. This system makes locations, sizes, and directions between all map’s features to be highly accurate. The main problem with the UTM system is the fact that between main longitudinal zones directions are not true, they aren’t accurate. The problem is solvable; all it takes is making sure that all maps using the UTM system cover just one zone.
There are lots of different map projections used for different kind of maps, but the three main types shown here are the basics for mapping. Different types are better for different purposes, but all are used, more or less. At the moment, we just can’t make a map projection that’s 100 percent accurate, at least if using a flat 2D surface as a baseline. If using a globe, we can make an accurate world projection but for reasons previously stated, globes aren’t the best choice when it comes to classic maps. Some apps, like Google Earth, are able to show a map projection on a globe. You don’t have to carry it around, and can look at it from almost any smartphone, laptop or tablet, but for serious mapping, a globe isn’t very good a choice.