In MARC field 043 is a geographic area code that has a hierarchy.

http://www.loc.gov/marc/bibliographic/bd043.html
http://www.loc.gov/marc/geoareas/

An XML version is available for use in applications at:
http://www.loc.gov/standards/codelists/gacs.xml

"This document contains a list of geographic areas and their associated
one-to seven-character
codes. The list includes separate codes for countries, first order
political divisions of some countries,
regions, geographic features, outer space, and celestial bodies. The
purpose of this list is to allow
places reflected in the subject headings assigned to an item to be
designated by codes in the MARC
record for that item. The list contains 579 discrete codes, of which 51
are discontinued codes no
longer valid for use."

Sincerely,
David Bigwood
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Lunar and Planetary Institute