10  Spatial Primer

A quick primer for spatial concepts.

10.1 Key terms

  • Coordinate (curved): Coordinates are numerical representations used to determine the exact location of a point on the Earth’s surface. They are typically expressed as latitude and longitude within a specific coordinate system, which can be a Geographic Coordinate System (degrees of latitude and longitude) or a Projected Coordinate System (using linear units like meters).
  • Projections (flattened): A projection is a method used to represent the curved surface of the Earth on a flat map. It involves transforming geographical coordinates (latitude and longitude) from the Earth’s spherical surface to a two-dimensional map, handling distortions in shape, area, distance, or direction to suit different mapping needs.
  • Coordinate Reference System (CRS): A CRS is a framework used to define how spatial data is geometrically represented on the Earth. It combines a coordinate system (defining how points are plotted) with a map projection (determining how these points are flattened onto a map). This unified setting ensures spatial data aligns accurately with real-world locations.

10.2 Common Coordinate Reference Systems

  • Albers USA
    • EPSG:5070
    • st_transform(5070)
    • Albers USA is a CRS using the Albers Conic Equal Area projection and NAD83 datum, optimized for area-accurate thematic and distribution mapping across the conterminous United States with minimal distortion.
  • WGS 84
    • EPSG:4326
    • st_transform(4326)
    • Leaflet default CRS
    • EPSG:4326 is a geographic coordinate system using the WGS84 datum, standard for GPS and web-based geospatial data applications like Leaflet.
  • Web Mercator
    • EPSG:3857
    • st_transform(3857)
    • Default for mapbox
    • optimized for web mapping applications like Google Maps and OpenStreetMap, minimizing distortion for fast rendering and seamless zooming.”
  • NAD83 UTM 18N
    • NAD83 / UTM zone 18N
    • NAD83 / UTM zone 18N is a Coordinate Reference System that combines the North American Datum of 1983 with the Universal Transverse Mercator projection for precise mapping and data analysis in eastern North America.