There was a question in the Sql Server Spatial/Katmai forums
about why a straight line on a sphere didn't "look straight".
Katmai both have planar and spherical geometry types. The
spherical type makes it easier to handle things like straight
lines, distances and areas over large distances, and depending
on which type you choose, you can get very different results.
Consider traveling on a straight line from Vancouver to
Frankfurt. They are both located roughly at latitude 50°N. So
the line would follow latitude 50°N right? Well that's true for
a planar coordinate system: So according to The Flat Earth
Society (who actually believes the Earth is flat) the green line
above shows the shortest distance between the two cities. But
what we are actually seeing is an artifact of working with a
planar coordinate system depicting a world that is not planar.
Using a spheric coordinate system, we get a different result.
When looking at this line in a projected coordinate system, like
the Mercator projection I've used her