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- If two consecutive points have the same latitude value, then the line connecting the two points is a parallel on the surface of the Earth; this may be explicitly stated using words such as “along the parallel to” (for the detailed encoding see page Parallels);
- Otherwise, it is considered a “straight line on the map” (for the detailed encoding see page TBD Straight Line).
In addition, the source map used when the airspace was designed is typically unknown.
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