Theadn Coordinates

From Sedes Draconis

The Theâdn coordinate system is the most standardized system in the Trade Culture. It was set out by Theâdn, a gnomish mathematician around 620 GR. Note that it is not widely used, most people navigate by routes, not abstract coordinate systems. But since it is the most systematic way of describing location, it is used for this site.

Latitude is divided into two quarter circles (gnomes divide a circle into 144 parts, called "degrees" here for convenience, see also Unit Conversion) measured out from the poles. So each pole is at 0°, North and South, and the Equator is 36° latitude.

Longitude is measured from East to West in a full circle (144°) with the zero point at Ghelth. So the 36th line is just east of Tâl Katar , the 72nd line passes just west of the Khiltor Archipelago, and the 108th line passes through Thorvik to the eastern edge of the Gulf. These four lines define the four Quadrants that are used to refer to generally areas. (Note these are not the same as the four pieces of the Map of the Hajasith.) The Quadrants are the most widely used aspect of the system, and in the last century have become the primary description of region (and intra-regional direction) used by the gnomes. In the past 70 years, non-gnomes have increasingly adopted this usage.

The standard way of referencing a Theâdn coordinate is as follows: Latitude is referred to in as "degrees out". Ex: Tâl Katar is a little more than two degrees out. Often times "degrees" is dropped. Longitude is referred to as "lines". Ex: Tâl Katar is just passed the 72nd line.

So Tâl Katar's location would standardly be refered to as "two (degrees) out, on the 72nd line".

Since Theâdn coordinates are used only on the Hajasith at this time, there is little need to distinguish which hemisphere a latitude coordinate refers to. But when necessary "degrees out from North", or distinguishes from "degrees out from South"; or just "from North", "from South".

http://www.sedesdraconis.com/images/coord.jpg

Note that the conventional orientation of a map of the Hajasith by itself is oriented with the 0th line diagonalling off to the left. This makes the relation of that map (part of an Azimuthal equidistant projection) to the Mollweide projection map above, where the 0th line goes down and to the right somewhat counter-intuitive. The full world (Mollweide) projection above is obviously based on the pure math of the Theâdn coordinate system. The Hajasith map is most often drawn as it is because it fits most neatly in a rectangular area, a convention that was already prevalent by the time the coordinate system came to be used.

Though no gnome has ever been further than 15° from the North Pole, that proximity, combined with knowledge gained from the kobolds, has made the calculation of the earth's circumference, and thus the lines of latitude, a relatively easy calculation. Relatively.