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Nat's remark about reducing the size of a map (and therefore the scale)
using a copier reminded me of one issue we attempted to address in our
search for a suitable map copier--distortion.
 
We found that most vendors hadn't the faintest idea how much their machine
did or did not introduce distortion.  Because some of our library
customers may be taking measurements or will be mosaicking several maps
together, this was an important consideration.  Sorry I can't shed much
technical light on the subject, but its a good question to ask.
 
After we bought our black and white Dietzgen we threw a copy over an
original for a light table comparison.  We found negligible distortion.
I imagine that any copier with a linear scanning sensor will do okay.
Watch out for smaller machines with a single zoomable lenses (such as found
on most document copiers)--I wouldn't use those copies for anything except
reference.
 
mark
 
ps. Remember to copy the bar scale with the map when reducing or enlarging.
The representative fraction won't be much use after the scale has changed.