Cartographic Projection

Overview Cartographic projections are mathematical transformations that convert three-dimensional positions on the Earth's surface into two-dimensional coordinates on a flat map. Since it is impossible to flatten a curved surface without some form of distortion, every projection involves trade-offs between preserving different spatial properties. The discipline of map projectionMap ProjectionMap projections are mathematical transformations that convert the three-dimensional surface of the Earth onto a two-d... theory addresses how to minimize and manage these distortions for specific mapping purposes.

Projections are classified by the geometric surface used in the transformation. Cylindrical projections (Mercator, Transverse Mercator, Miller) wrap the Earth in a cylinder and produce rectangular maps well-suited for equatorial and worldwide views. Conic projections (Lambert Conformal Conic, Albers Equal-Area Conic) project onto a cone and work well for mid-latitude regions with east-west extent. Azimuthal projections (Stereographic, Orthographic, Gnomonic) project onto a plane from a single point and are ideal for polar regions and hemispheric views. Each family has characteristic distortion patterns determined by the projection surface geometry.

Projections are also classified by which spatial property they preserve. Conformal projections preserve local angles and shapes but distort area. Equal-area projections preserve relative sizes but distort shapes. Equidistant projections maintain true distances along certain lines. Azimuthal projections preserve directions from a central point. Compromise projections, like Robinson and Winkel Tripel, balance multiple properties without perfectly preserving any single one, making them popular for world maps.

Choosing an appropriate projection requires considering the map's geographic extent, location, purpose, and audience. Large-scale local mapping uses projections optimized for the specific area, such as UTM zones or State Plane. Thematic maps showing statistical data require equal-area projections for fair visual comparison. Navigation charts use conformal projections to preserve bearing accuracy. The growing availability of projection selection tools helps users choose optimal projections based on these criteria.