PS! Rainboe, I'm sure you meant to say that on a Mercator chart, great circle tracks are curved upwards towards the North pole (in the northern hemisphere), not towards the equator.
Quite right to pick me up! Rereading it, it can be seen as wrong. I was meaning 'curved towards' as one would mean it if one was travelling along it (as I spend thousands of hours doing!), not that the curve is viewed as curved down towars the equator....... Still doesn't get much clearer- I should have used 'concave to' and 'convex to' the equator! I know what I mean anyway!