Abstract
Map projections are one of the foundations of geographic information science and cartography. An understanding of the different projection variants and properties is critical when creating maps or carrying out geospatial analyses. The common way of teaching map projections in text books makes use of the light source (or light bulb) metaphor, which draws a comparison between the construction of a map projection and the way light rays travel from the light source to the projection surface. Although conceptually plausible, such explanations were created for the static instructions in textbooks. Modern web technologies may provide a more comprehensive learning experience by allowing the student to interactively explore (in guided or unguided mode) the way map projections can be constructed following the light source metaphor. The implementation of this approach, however, is not trivial as it requires detailed knowledge of map projections and computer graphics. Therefore, this paper describes the underlying computational methods and presents a prototype as an example of how this concept can be applied in practice. The prototype will be integrated into the Geographic Information Technology Training Alliance (GITTA) platform to complement the lesson on map projections.
Highlights
Map projections are a key concept in cartography and geographic information science
The prototype illustrates that the proposed way of constructing map projections based on a real-time implementation of the light source metaphor is feasible and, as such, complements the more conventional approach of existing libraries based on tailored formulas
Allowing interactively constructing map projections in a 3D environment as provided by the described projection tool goes beyond the common static approaches provided by conventional educational resources
Summary
Map projections are a key concept in cartography and geographic information science. Choosing an inappropriate map projection may cause severely flawed results when carrying out geospatial analyses (e.g., when buffering in an inappropriate projected coordinate system [1]) or may distort a map reader’s view on the world when exploring a thematic or topographic map. Mapping software typically implements the projection process as a set of equations that can be applied to a point in geographic coordinates to obtain its projected coordinates Examples for this approach can be found in kartograph.js [2], d3.js [3], or Flex Projector [4]. Educational resources tend to follow a more figurative approach to explain the underlying geometrical meaning of the projection process This construction process typically starts with a projection center that can be imagined as a light source (or light bulb) placed in the proximity of (or within) the globe and emitting light in all directions. The radius from the shape’s center to the center line of the tube and the radius of the tube itself along with the scaling, enable creating all shapes such as spheres, discs, bars, and tori
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