Gall–Peters projection

The Gall–Peters projection is a rectangular, equal-area map projection. It is a way to represent the spherical Earth on a flat surface. Like all map projections, it must deal with distortion. Because the Earth is a sphere, you cannot flatten it without changing something. This specific projection is a cylindrical equal-area projection. This means it prioritizes the correct size of landmasses over the correct shape of continents.

To understand how it works, imagine a cylinder wrapped around the Earth. The map is created by projecting the surface of the sphere onto this vertical cylinder. In the Gall–Peters version, the cylinder is stretched to double its length. This stretching is a specific mathematical process. It ensures that the area of any region on the map matches its true relative size on the globe. This type of map is known as an equal-area projection. However, this accuracy comes at a cost. The shapes of landmasses become highly distorted, often appearing stretched vertically.

The projection does not distort everything equally. There are specific regions where the map is most accurate. These are called standard parallels. For the Gall–Peters projection, the standard parallels are 45° N and 45° S. Along these two lines, there is no distortion. At these latitudes, both shapes and distances match the stated scale. As you move away from these lines toward the equator or the poles, the shapes change more significantly.

The history of this map involves two different men. James Gall, a Scottish clergyman, first described this projection in 1855. He presented it at a science convention in Glasgow. He later published a formal paper on it in 1885. He originally called it the "orthographic" projection. Much later, in 1967, a German filmmaker named Arno Peters created a similar projection. He introduced his "Peters World Map" to a wide audience in 1973. The combined name, Gall–Peters, was first used by Arthur H. Robinson in 1986.

Arno Peters made the map famous through a major controversy. He argued that common maps, like the Mercator projection, were politically biased. He claimed the Mercator projection made wealthy areas like Europe and North America look too large. Meanwhile, he said it made poorer regions like Africa and South America look too small. Peters promoted his map as a superior alternative for social justice. He even claimed it was the only "area-correct" map. These claims were inaccurate, as many other equal-area projections existed.

The cartographic community responded with significant hostility. Experts criticized Peters for his inaccurate claims about the map's properties. They noted that his map had extreme distortions of shape. They also pointed out the irony of his map. It showed the mid-latitudes, including Peters's native Germany, with little distortion. However, it distorted the low latitudes where many developing nations are located. This led to a deep divide between Peters's supporters and professional map makers.

Despite the scientific debates, the Gall–Peters projection remains widely used today. It is promoted by UNESCO to help people visualize the actual relative sizes of global regions. Many schools in the United Kingdom use it as a standard tool. In the United States, Boston Public Schools began using these maps in 2017. Recently, the state of Nebraska passed a law in 2024. This law requires public schools to display the Gall–Peters projection or a similar equal-area map. It continues to serve as a tool for teaching the scale of our world.