PrintUnlike Earth, maps are flat. Though Earth can also be represented as a globe, globes are inconvenient, expensive, and challenging to design. Maps are much more convenient: they are easier both to produce and to reproduce, and when you are mapping detailed data at a relatively large scale, the Earth appears to be more or less flat anyway. So when you want to transform latitude and longitude values from the three-dimensional Earth onto a two-dimensional surface (a map), you will use a process called map projection.
In the past, cartographers were tasked with projecting maps by hand, necessitating relatively complex mathematical calculations. Fortunately, GIS software such as ArcGIS is now able to perform this task of projection for us automatically. Though deriving a map projection through manual methods is uncommon today, map projections are still being refined and invented– as one example, Bojan Šavrič (Esri), Tom Patterson (US National Park Service), and Bernhard Jenny (Monash University) released the Equal Earth Projection in 2017.
To create a map, cartographers transfer a model of the earth as it appears on a reference globe to a developable surface.
A reference globe is a model of Earth, including landmasses, oceans and the graticule (lines of latitude and longitude), at some chosen scale, which is the final scale of the map to be created (Slocum et. al 2023). This projected map is thus modeled from an imaginary scaled-down version of Earth.
A developable surface is a mathematically-definable surface onto which landmasses and the graticule are projected (Slocum et. al 2023). In simpler terms, a developable surface is any surface that can be “unrolled” flat and thus, create a two-dimensional map. Typically, this surface is described as a cone, a plane (flat surface), or a cylinder. In this next section, we discuss how the choice of a developable surface—among other factors—influences a map projection's characteristics.
Student Reflection
Imagine the cone developable surface as a party hat placed on top of Earth. After projection, which locations do you imagine would appear the least distorted on the resulting map? Which would appear the most distorted?
Recommended Reading
Chapter 8: Elements of Map Projections. Slocum, Terry A., Robert B. McMaster, Fritz C. Kessler, and Hugh H. Howard. 2023. Thematic Cartography and Geovisualization. 4th ed. Boca Raton, FL: CRC Press.