District geocodes

The Department of provincial administration (DOPA) uses a list of geocodes for each of the provinces, districts and subdistricts, modeled after the ISO 3166-2 codes of the provinces. Newly created entities get a number following the existing ones of course, though not necessarily in the same order as the official creation as the geocode already gets assigned when the district is in the planning phase. However when that list was started, the numbers of the then-existing districts wasn't created in a simple alphabetical order, or in creation order.

Minor districts were a partial subordinate of the district from which they were created, so in official texts they are referenced as "King Amphoe ..., Amphoe ..., Changwat ...". For the same reason they got assigned a number directly following their master district. Thus with the oldest new districts added at the end of the geocodes instead of directly after the master allows it to date when this geocode list was started. Chai Buri, created in 1981, got the 8418, but Phunphin (the 8417) wasn't its master, so these geocodes were started around 1980 already. Minor districts created in 1978 however are sorted after their master district.

The odd thing about this timing is the fact that the first draft of the ISO 3166-2 standard with geocodes for the provinces of 1988 was based on the US-created FIPS, and not the apparently already existing codes from DOPA. Also in the 1990 census a different geocode system was used, but for the 2000 census the DOPA system was also adopted by the census department. The ISO standard was officially published in 1993, then based on the DOPA system. Also in the 2000 census the DOPA geocodes were used.