|The Great Caldera, Equirectangular Projection|
The result of a massive collision in Calidar's ancient history, the Great Caldera is a perfect circle with a mountainous rim. This presents a unique mapping challenge: drawing a circle on a sphere is easy, but the rectangular map projections usually used to design worlds are another matter entirely.
The 2:1 latitude/longitude grid known as Equirectangular, Plate Carrée, or simply Geographic Projection is very useful because it is easily applied to 3D spherical models, such as Google Earth. But the further north or south you go, the more stretched it becomes, until the entire top and bottom lines of the map represent the single points of the poles.
The Great Caldera stretches from 25º to 65ºN, putting the northern part of the Caldera in an area which is very susceptible to these distortions.
Look closely at the first map. Does it look like a perfect circle to you? Probably not. But in fact it is a perfect circle when viewed on a globe.
|The Great Caldera, Stereographic Projection|
The Stereographic Projection is particularly appropriate for the Great Caldera, because it shows any circle on the globe as a circle on the map.
If we had just drawn a circle on the Equirectangular Projection base map, it would have ended up being deformed when viewed on a globe. These days, when it's very easy to set up Google Earth or a number of other programs to display interactive globes in the computer, it was a design priority to get these projection issues right from the start.
Getting back to the map, you can see how the perfect circle of the Great Caldera has collapsed and decayed at various points. We'll take a look at the design phase for the mountains encircling the Caldera in the next post.
|The Great Caldera (Uncorrected Version), Equirectangular and Stereographic Projections|
This last map predates the first two, showing the same design for the Great Caldera, this time as a political map showing borders and country names. The inset shows Bruce's original design, which we did on an Equirectangular Projection (as many mappers do, since it allows the aforementioned use of Google Earth). It looks fine – a perfect circle. The problem with this is that when it is applied to a globe or other 3D spherical model, the Caldera's shape is deformed, appearing more like it looks in the Stereographic Projection.
So the first two maps above are the result of a proper implementation of this design, as Bruce originally intended it to look. One last map to illustrate my point: this rendering of the globe of Calidar was made using an Equirectangular Projection world map. Note how the Great Caldera looks nice and circular, as it is supposed to.
|The World of Calidar, Orthographic Projection (also known as "View from Space")|