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 - see language/country name servers). 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 -> - displaynameTwo-letter codes for administrative subdivisions are also usual in Canada, Switzerland, Italy, and defined but rarely used in China, Germany, etc. (Others: please add!) For France, one might use the two-digit departement codes as used on number plates (e.g. 13: Bouches du Rh�ne (Marseille); 75: Paris).
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 resolve 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 AmericaOne 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 = Europeand 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.
Geographic mapping the Tcl way - Arts and crafts of Tcl-Tk programming