Ms. Quill,
I think that you need to answer the question of what makes a map "rare" in
your collection.  Why does the map need to be under controlled access?

There are several reasons why materials are under controlled access, but
they tend to add up to being at some sort of risk.  The map(s) and atlases
might have a high monetary value.  We've all heard of map thefts in the
last few decades.  The item might be rare but not particularly monetarily
valuable.  A manuscript map of a local area or a plat for the town where
you are situated could fall in such a circumstance, even a "published map"
that exists in relatively few copies.  Sometimes maps might be at risk for
political reasons because they are evidence for or against a claim to
possession.
Then there are maps that are at risk because they are fragile and
currently irreplaceable even if there once were many exemplars.  A map
might demonstrate an unusual method of production even if the territory
mapped is not very "special."
Sometimes maps are important because they are one piece of a very much
larger collection that documents changes over time.  Outdate topo maps can
fall into this category.  For example, we are interested in old versions
of NM topo maps but not interested in older Texas maps.

As others have pointed out, you have to make those decisions in the
context of your overall collections and situation.

Good luck,
Larry
-- 
Laurence S. Creider
Head, Archives and Special Collections Dept.
University Library
New Mexico State University
Las Cruces, NM  88003
Work: 575-646-4756
Fax: 575-646-7477
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On Thu, October 16, 2014 12:15 pm, Theresa Quill wrote:
> Hi all,
>
> I'm in the middle of revamping what we consider "rare maps" and I was
> wondering if y'all have policies that spell out which maps are "rare". Do
> you do it by date? If so, what is your cutoff? Number of copies in the
> world? Relevance to your institution?
> For example, the USGS 15 and 30 minute topos are OLD but not necessarily
> RARE. We also have some newer maps that we hold the only cataloged copy
> for. So maybe there's a hybrid solution? If you do have a policy, would
> you
> mind sharing it?
>
> Thanks!
>
> --
> Theresa Quill
> Map/GIS Coordinator, Herman B Wells Library
> MLS Candidate, School of Library and Information Science
> Indiana University
>