You think this an odd title, a square is a square. Well
whilst that is the case in a planar 2D world in a 3 spatial world where the
square is drawn on a sphere.
This is one of the areas that catches most people out.
If you define a polygon with corners at (0,0) (0,50) (90,50) (90, 0).
So this starts on the equator at Greenwich and then moves north until the 50
longitude, then moves to a point a quarter round the world again on longitude 50
and back to the equator on latitude 90.
On first glance you would think that the line from (0,50) to (90,50) follows
ring that defines longitude 50, and this is the error. The line between these
two points is actually the shortest distance between, which is part of
great circle. Morten has done a great blogpost on this Straight lines on a sphere .
What is a shame is that both Mortens Shape to Shapefile to SqlServer 2008 to
WPF and Virtual earth both draw the polygon as though it
followed the ring of longitude. What this leads to is confusion over when shapes
intersect
If you are likely to be working with Spatial data covering the earth I
suggest you buy a globe to enable you to visualise the world.