Part 2 Edinburgh grid geometry continued

continuing with the exploration of the Edinburgh grid:

In the previous post the basic orientation of the street plan of Edinburgh New Town was shown.  My interest was drawn to this originally when it w, as noticed that the line from the pentagram maze at Old Scone was on the line that had started this research over twenty years ago, and that the Craig plan for Edinburgh appeared to be linked closely to it!  When starting from the grid plan orientation it was found that the exact(to the one-hundredth of one degree using Google Earth) bearing (plus 90degrees) from the pentagon at Old Scone passed over Calton Hill, through the Observatory there and is shown in the last image in the previous post, and again below:

Now this line has some interesting points on it, but it is some two-three hundred yards west of my original, and needs some investigation!

The astonishing thing is that this orientation runs straight to Mavisbank eart works which features so strongly in the previous investigation!  This line also includes a hill fort or whatever near Perth, unmarked on GE, and also the main road junction in the village of Scotlandwell on at the foot of Bishop Hill near the edge of Loch Leven, and also Liberton Kirk which is a good sighting point to the south of Calton Hill!

Using Calton Hill to Liberton kirk as a test of what happens more locally in GE a slight discrepancy appears:

so my guess is, its perhaps an artefact of GE, and whether its best to have the lines 'clamped to ground' or relative to ground' which are options in GE.  Relative hights may also be a factor, although Calton Hill and Liberton kirk are roughly equal in altitude, but Old Scone is lower and at a distance of some 45miles or so, the earth's curvature may start to be a factor!?  Something I have wondered about when working at large scale. Straight single lines are not an issue but geometry on the sphere angles become distorted somewhat, and my math skills don't stretch to that!