[Richard Suchenwirth] - In [Tclworld] I want to have much and detailed geographic data, both
for display on the map and for browsing additional facts. In this process I notice that not all
geographic names are unique - which would be required for using them as array indices in the 
database. A city named '''Hamilton''' exists for instance in England, but also in Australia, Canada, 
New Zealand (colonialists sometimes have limited imagination ;-), as well as in the US states of
Alabama, Montana, and Ohio. In the US case, the typical solution is to append the state name, often
in the two-letter USPS abbreviation. For the countries of the world (and dependent territories), there
are also two-letter codes in ISO 3109(?), but not disjoint from the US state codes (e.g. CA is both
California and Canada). However, one could introduce a hierarchic scheme, e.g. from specific to 
generic, like Web domains:
 Hamilton,GB
 Hamilton,OH.US
or, for having the tree structure clearer (e.g. in sorted lists):
 GB;Hamilton
 US.OH;Hamilton
in which the semicolon marks the place where the "display name" (to be put on the map, or database
browser) begins - which is easily extracted with the [regexp]
 regexp {(.+;)?(.+)} $qualifiedname -> - displayname
Two-letter codes for administrative subdivisions are also usual in Canada, Switzerland,
Italy, and defined but rarely used in China, Germany, etc. (Others: please add!)

Resolution of such "fully qualified pathes" could be done with database entries like
 + GB = {Great Britain}
 + US = {United States of America}
 + US.OH = Ohio
(+ is an alias for the database, to make these lines valid Tcl commands - see [A simple database API]). 
Here's how to translate such geocodes to human-readable:
 proc explain {db code} {
    set res ""; set region ""; set name ""
    regexp {(..)([.]([^;]+)(;(.+))?)?} $code -> country - region - name
    if {$name!=""} {append res "$name in "}
    if {[set dbRegion [$db $country.$region =]] != ""} {
        set region $dbRegion
    }
    if {$region!=""} {append res "$region, "}
    if {[set dbCountry [$db $country =]] != ""} {
        set country $dbCountry
    }
    append res $country
 }
 % explain + GB
 Great Britain
 % explain + US.OH
 Ohio, United States of America
 % explain + "US.OH;Hamilton"
 Hamilton in Ohio, United States of America

One might consider a level above countries, which would of course be '''continent'''. One letter is too 
short, as the majority of continent names starts with A, so for instance
 + AFR = Africa
 + AMN = {North America}
 + AMS = {South America}
 + ANT = Antarctica
 + ASI = Asia
 + AOC = {Australia & Oceania}
 + EUR = Europe
and a pedant might even construct "fully qualified names" like this:
 Terra.AMN.US.CO.Denver
to be prepared for interstellar extensions - but we better keep the data compact, and using the country
code as "top-level domain" should be sufficient for the foreseeable future.

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[Geographic mapping the Tcl way] - [Arts and crafts of Tcl-Tk programming]