District levels

In a German blog I found the reference to the new Google Guru, which is only available in Thai (and now also in Arabic). I took a look for questions concerning Tambon or Amphoe, and among several questions "How many Amphoe in Province XYZ", one question around Amphoe was really interesting.

อำเภอในประเทศไทยมีกี่ชั้น แต่ละชั้นใช้เกณฑ์อะไรในการแบ่งชั้น
How many levels of Amphoe in Thailand, and what are the criteria for each level?

While I heard about the different levels of the Subdistrict Administrative Offices (TAO), I did not know about the district having different levels - except the minor districts (King Amphoe), which until they were all upgraded in 2007 were a lower class of districts.

So naturally I tried to find a list of the levels and which Amphoe belong to which level. However it seems there's hardly anything online on these levels, the only tabular thing I found was a PowerPoint presentation from 2004, in which it has the following table

• Special districts (อำเภอชั้นพิเศษ): 17 districts
• Level 1 districts (อำเภอชั้น 1): 161 districts
• Level 2 districts (อำเภอชั้น 2): 229 districts, 1 minor district
• Level 3 districts (อำเภอชั้น 3): 220 districts, 6 minor districts
• Level 4 districts (อำเภอชั้น 4): 167 districts, 74 minor districts

Though two slides later it lists the criteria, I don't understand them as it only says something about "raw score" and can only guess that its some kind of economic score which is used as the basis for the district level. Only thing I can understand is that the Mueang districts are always either level 1 or special level.

And for the special districts I could find a list in a document which looks like the answer sheet to a entrance test for officers in the local administration. According to that file, the special districts are the following:

Mueang Khon Kaen, Mueang Chonburi, Mueang Chiang Mai, Mueang Nakhon Pathom, Mueang Nakhon Ratchasima, Mueang Nakhon Si Thammarat, Mueang Nonthaburi, Mueang Phitsanulok, Mueang Phuket, Mueang Rayong, Mueang Lampang Mueang Samut Prakan, Mueang Surat Thani, Mueang Udon Thani, Mueang Ubon Ratchathani and Hat Yai.

So yet another posting without a complete answer, anyone who can help me to a more complete one is welcome...