NavList:

I was reviewing what I’d written in this thread and spotted that I’d been guilty of sloppy writing in this post http://fer3.com/arc/m2.aspx/Sun-does-not-stop-for-anyone-DavidPike-dec-2016-g37557 , which either no-one noticed at the time or they were too well mannered to pick me up on.  I said:

If you follow the link, you’ll see the meridians and parallels don’t go straight up and down and across the cut of the chart, but they do cross at right angles, so the chart is still conformal. 

This of course was wrong.  Although it is true that on a conformal chart the parallels and meridians cross at right angles, the reverse is not necessarily true.  You can only say that if the parallels and meridians cross at right angles a chart might be conformal.  The real test for conformity is that the scale at any point must be the same in every direction. E.g. the geometric cylindrical projection which we have talked about a lot recently does have parallels and meridians crossing at right angles, but it is not conformal.  DaveP