3 ms·
That's an excellent question. Latitude and longitude are straight in the projection he is most likely using, but great circle arcs are what we consider straight
by adolgert 13y ago
That's an excellent question. Latitude and longitude are straight in the projection he is most likely using, but great circle arcs are what we consider straight on the globe. The kicker is that most political boundaries are neither. They are Rhumb lines, aka loxodromes, which mean that someone started walking in a direction and kept going.
The standard solution for this is to put lots of little points into the state GIS definition, so that the points get transformed correctly. That way short line segments don't differ by more than a few meters. That means you have to watch out for simplified state representations, but not much else, unless you're being a stickler.
- waqf 13y ago> Rhumb lines, aka loxodromes, which mean that someone started walking in a direction and kept going. To be clear, they mean that you keep going in the same compass direction. If you kept going in the direction which seemed straight ahead to you there on the ground, then what you'd get (under suitably idealized conditions) is a great circle.
- tantalor 13y agoLocally, it would zig-zag all over the place, like the US-Canada border: http://www.youtube.com/watch?v=qMkYlIA7mgw http://www.youtube.com/watch?v=qMkYlIA7mgw