[Qgis-user] Help with scales in print layouts for geographic CRS

[Greg Troxel]

A further suggestion, which may be too much.

UTM, and the various LCC used in the US at State Plane Coordinate
Systems, have x/y coordinates that are nominally in meters (well, the
older ones used ft or ftUS).  Central meridian or standard parallel
scale factors are chosen to make distance measurements on the ground
correspond to cartesian distances calculated from project coordinates.

When printing UTM maps, standard practice as I understand it is to use a
scale such as 1:25 000, where 1 mm on the map is 25 m in cartesian
distance in projected coordinates.  So the 1 km grid lines would be 40
mm apart.  This is true even if the map is near the edge of the UTM zone
(or in the center).

So, it makes sense to treat a layout in UTM such that scale means the
previous paragraph, even though it's off slightly from my previous
suggestion.  I view this as scale being sort of "snap to standard" if
close.

With quality projections, I suspect this is a difference that might not
be perceptible, but in thinking of printed maps in UTM at standard
scales being used with transparent overlay rules to read coordinates for
search and rescue, I think it makes sense to be able to match this
practice.
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