Map Projection Types: Conformal, Equal-Area, & Equidistant
A map projection is a mathematical transformation that flattens Earth's curved 3D ellipsoidal surface onto a 2D plane. Carl Friedrich Gauss's Theorema Egregium proved that it is physically impossible to flatten a sphere without stretching, tearing, or distorting its surface.
The 3 Primary Projection Families
| Family | Surface Shape | Best For | Examples |
|---|---|---|---|
| Cylindrical | Cylinder wrapped around sphere | Global maps, navigation, Web Mercator | Mercator, Transverse Mercator (UTM), Gall-Peters |
| Conic | Cone placed over pole/region | Mid-latitude countries (USA, Europe) | Lambert Conformal Conic, Albers Equal Area |
| Azimuthal (Planar) | Flat plane touching sphere at a point | Polar regions, radio propagation, aviation | Stereographic, Gnomonic, Orthographic |
Preserved Distortion Properties
- Conformal (Orthomorphic): Preserves local angles and shape (e.g. Mercator, Lambert). Essential for navigation and surveying.
- Equal-Area (Equivalent): Preserves relative land area ratios (e.g. Albers, Gall-Peters). Essential for thematic density maps.
- Equidistant: Preserves true scale distances along specific meridians or lines.