I have just been georeferencing a map on QGIS using British National Grid and it is not lining up with the vector maps I downloaded from OS. I used the 'From map canvas' option and used 'Linear' transformation. However, there appears to be a twist of a few degrees with the map and this suggests that the one is setting as grid north and the other magnetic which would explain the difference. I tried a few times with different reference points, but always the same result.
Anyone any ideas?
Ok, just to add. I rotated the original image by 1.5 degrees and then re-georeferenced and it near enough lined up. Surely the idea of georeferencing would be to put the points in the right place no matter what the orientation of the original raster map?