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Roger,
 
You may consider that the 'drawing process' (drawing, printing,
and paper quality) allows for an accuracy of 0.1 millimeter.
Therefore the 'ground resolution' of such a map is 5 meters.
The general formula being a/S where a stands for map accuracy
and S for scale.
However two other facts need to be taken into account:
- first, a map provides a symbolized graphic representation,
features are symoblized using lines, point symbols... which implies
that something which is initially abstracted by a mathematical line
becomes a thick line etc... For example road casings  may be 0.2 mm
wide. As a consequence cartographic generalization has been applied,
which induces a larger ground resolution in some places (you may
consider 10 meters on the average, but it may be larger)
- second, the scanner accuracy depends on the fact that you scan
multiple colors at once (scanning of a paper map), or each color film
separately, because the scanners have some limitations. You may need
to use a finer resolution when scanning a paper support, or rather
a smaller ratio scanning resolution / map resolution.
 
JPhilippe Lagrange
IGN-F