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Understanding Map Projections in GIS: From Geographic Coordinates to Planar Maps

In the field of Geographic Information Systems (GIS), maps are considered much more than a graphical representation of the Earth's surface; they provide accurate spatial representation for analysis, planning, and decision. However, the difficulty stems from the fact that while the Earth is spherical, maps are flat and projecting three-dimensional geographic data onto a two-dimensional surface is described as the process of map projection.


Map Projections in GIS
Map Projections in GIS

What are map projections?


A map projection is a mathematical transformation that converts the geographic coordinates (latitude and longitude) from the Earth's curvature into planar coordinates (x,y) for mapping and analysis.


Given that it is impossible to "perfectly" flatten a sphere without some distortion, all projections will have some level of directional accuracy. The distortion can be with respect to shape, area, distance, or direction and knowing which properties will be preserved versus being distorted will allow GIS practitioners to select appropriate map projections for analysis.


The Importance of Map Projections in GIS


In GIS, accuracy is paramount. The projection you select can affect how well the spatial data aligns, how measurements are conducted, and how analytical results are interpreted. Consider the following examples:


  • A projection that is designed for navigation may preserve direction but distort area.

  • A projection that is designed for thematic mapping may preserve area but distort shape.

  • A projection designed for local mapping may not be suitable for global data.


If you are using an incorrect projection, the data may be misaligned, displayed at the wrong scale, or analysis may lead to misleading and incorrect results.


Common Map Projections


Maps may be broadly categorized by how they project the Earth’s surface:


  1. Cylindrical Projections


These projections may represent the Earth by wrapping a cylinder around the globe.

Example: Mercator projection


  • Preserves direction (conformal)

  • Distorts the area in high latitude regions

  • Commonly used in marine navigation/transcontinental navigation and web maps (i.e., Google Maps)


  1. Conic Projections


These projections place a cone over part of the Earth. Example: Albers Equal Area Conic

  • Minimizes distortion in mid-latitudes

  • Ideal for mapping countries or regions (like the U.S.)

  • Often used for thematic or statistical maps.


  1. Azimuthal (Planar) Projections


These project the globe onto a flat plane, touching the Earth at a single point.Example: Lambert Azimuthal Equal-Area Projection

  • Preserves direction and distance from the center point

  • Ideal for polar maps and airline route planning


Understanding Properties of Projections


A projection can preserve just one or two of the following properties at a time:


  • Conformal (Shape Preserving): Preserves local angles or shapes in a local area (Mercator)

  • Equal-Area (Area Preserving): Preserves true proportions of area (Albers Equal Area)

  • Equidistant (Distance Preserving): Preserves true distances from a set point or line

  • Azimuthal (Direction Preserving): Preserves true direction from a point

  • Choosing a projection depends on the intent of your map and the geographic area being mapped.


Coordinate Systems and Projections


A coordinate system defines how the map projection will translate geographic coordinates to planar coordinates.


  • Geographic Coordinate System (GCS): This is latitude and longitude in degrees, based on a reference ellipsoid, such as WGS 84.

  • Projected Coordinate System (PCS): This is the GCS in a flat 2D map by projecting it using a projection method such as UTM or State Plane


When working with spatial data, make sure to always note what the CRSs are for your dataset, to ensure each of your layers will line up.


Selecting a Suitable Map Projection in GIS


When selecting projections, keep in mind:


  1. Intention for the Map: Is it for navigation, analysis, visualization, or measurement?

  2. Geographic Extent: Is it a global, continental, or local extent?

  3. Preserved Property: Which is more important, shape, area, distance, or direction?


For example:


  • Use of Mercator for navigation (maintains direction).

  • Use of Albers Equal Area for the presentation of thematic or statistical maps.

  • Use of UTM (Universal Transverse Mercator) for accuracy for local engineering or planning purposes.


The Role of Map Projections in Modern GIS


Modern GIS software like ArcGIS Pro, QGIS, and Google Earth Engine allows users to easily reproject spatial data. However, knowing your projections is an important step to ensure spatial accuracy while combining or analyzing geospatial datasets.


Making the right projection choice ensures the data integrity of your data, the accuracy of your measurements, and the validity of your visualizations.


It is important to know about map projections in GIS to accurately convert geographic coordinates into a planar display. Every projection has strengths and weaknesses, but once you understand their characteristics and best uses, the GIS user can make an informed choice that improves both analysis and visualization.


Whether you develop a basic map or conduct advanced spatial analysis, the understanding of projections enables you to interpret neutral geographic data into meaningful geographic information.


For more information or any questions regarding map projections, please don't hesitate to contact us at


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