Map Projection

Map projections are fundamental to cartographyCartographyCartography is the practice of designing and producing maps to visually represent spatial data. It serves diverse pur... and GISGISGeographic Information Systems (GIS) enable users to analyze and visualize spatial data to uncover patterns, relation..., enabling the representation of Earth's curved surface on flat maps and screens. Since no projection can perfectly preserve all spatial properties simultaneously, understanding map projections is essential for anyone working with geospatial dataGeospatial DataGeospatial data encompasses information about the location, shape, and relationships of physical features on Earth. I.... The choice of projection directly affects measurements of distance, area, shape, and direction, making it one of the most consequential decisions in any mapping project.

Map projections are generally classified by the geometric surface used in the transformation and the spatial properties they preserve. The three primary projection surfaces are cylindrical, conic, and azimuthal (planar). Cylindrical projections, such as the Mercator projectionMercator ProjectionThe Mercator projection is a cylindrical conformal map projection that preserves angles and shapes locally, making it..., wrap a cylinder around the globe and are commonly used for world maps and navigation charts. Conic projections, like the Lambert Conformal Conic, project the globe onto a cone and work well for mid-latitude regions. Azimuthal projections project from a single point and are ideal for polar regions or mapping hemispheres.

Every map projection involves trade-offs among four key properties: shape (conformality), area (equivalence), distance (equidistance), and direction (azimuthality). Conformal projections like Mercator preserve local shapes and angles but distort area, especially near the poles. Equal-area projections like Mollweide preserve relative sizes of regions but distort shapes. Equidistant projections maintain accurate distances along specific lines, while azimuthal projections preserve directions from a central point. The Tissot indicatrix is a common tool for visualizing distortion patterns across a projected map.

Map projections are used across virtually every geospatial discipline. Navigation systems rely on conformal projections to maintain accurate bearings. Thematic mapping and demographic analysisDemographic AnalysisDemographic analysis examines the statistical characteristics of populations—including age, income, education, househ... require equal-area projections to ensure fair visual comparisons between regions. The Universal Transverse Mercator (UTM) system divides the world into zones, each using a transverse Mercator projectionMercator ProjectionThe Mercator projection is a cylindrical conformal map projection that preserves angles and shapes locally, making it... optimized for local accuracy, and is widely adopted in military, engineering, and surveying applications. Web mapping platforms like Google Maps and OpenStreetMapOpenStreetMapOpenStreetMap (OSM) is a collaborative, open-source mapping project that creates a free, editable map of the world. B... use the Web Mercator projection for its computational simplicity and seamless tiling.

Map projections enable the practical visualization of global data on flat media, support spatial measurement and analysis in GISGISGeographic Information Systems (GIS) enable users to analyze and visualize spatial data to uncover patterns, relation..., and allow cartographers to tailor maps to specific purposes by selecting appropriate distortion trade-offs. Modern GIS software makes it straightforward to reproject data between different coordinate systemsCoordinate SystemsCoordinate systems standardize the description of geographic locations using latitude, longitude, and other spatial d..., enhancing interoperability.

Selecting an inappropriate projection can introduce significant measurement errors. Many users are unaware of projection-related distortions, leading to misinterpretation of spatial relationships. Additionally, reprojecting large datasets between coordinate systemsCoordinate SystemsCoordinate systems standardize the description of geographic locations using latitude, longitude, and other spatial d... can be computationally intensive and may introduce rounding errors.

Advancements in web-based mapping have popularized adaptive projections that change dynamically based on zoom levelZoom LevelA zoom level is a discrete scale step in a web mapping tile system that determines the amount of geographic detail di... and geographic extent. Research into equal-area alternatives to Web Mercator is gaining momentum, and tools for automatic projection selection based on data extent and analysis type are becoming more sophisticated.