I think you should not use Dariv as the central place in the UTC+7 time zone. Take the more obvious Hovd. There are two Hovd in Mongolia, so you should add the alternative name Jargalant.

Jargalant is problematic. Rand McNally spells it Jirgalanta. Shanks spells it Dzargalant (with a hacek over the z), or as Chovd. The CIA spells it something like Duno-Us [...]

I have Dund-Us as the capital of Hovd province, with Hovd and Jirgalanta as older names which may still be in use for this city. Still older names include Khobdo and Kobdo.

We generally prefer the most populous location to represent a region, so we should use the most populous location in Hovd, Uvs, and Bayan-Olgiy. I suspect that the candidates are Jargalant (the capital of Hovd), Ulaangom (the capital of Uvs), and Olgiy (the capital of Bayan-Olgiy). Do you happen to know which is the most populous?

Looking in a 1980 Hammond atlas that I have at hand, I find the following populations for cities in the three provinces in question. They're out-of-date, but they may indicate relative sizes. Bulgan, Hovd 3,100 Dund-Us, Hovd 12,400 * Hyargas, Uvs 1,600 Olgiy, Bayan-Olgiy 11,700 * Tsagaannuur, Bayan-Olgiy 2,000 Tsetseg, Hovd 700 Ulaangom, Uvs 14,000 * It looks as if the three provincial capitals (*) are the only good candidates. Since ambiguity is a criterion for rejecting a location name, I checked the NIMA place names website. It has 6,161 records of populated place names in Mongolia, including variants. The NIMA database agrees with me about the preferred names of the three provincial capitals, as listed above. In the NIMA database, the names Dund-Us and Ulaangom are both unique. Among the other proposed names, Jargalant is the least desirable: there are 13 cities whose preferred names are Jargalant. There are three places whose preferred names are Hovd. There are two places named Olgiy, but one of them is a variant name for Har-Us. Darvi, not Dariv, is shown as a variant for Bulgan. There is a city named Dariv, but it's not in the new time zone. Doing some more research, I found the home page of the Mongolian National Statistical Office, at <http://statis.pmis.gov.mn/home_engl.htm>. There, I found the populations of the three capitals according to the 1989 census and an estimate for year-end 1998. 1989 1998 Dund-Us 24,100 27,400 Olgiy 27,200 21,000 Ulaangom 22,900 26,500 Following the published criteria, Dund-Us is the top choice, with Ulaangom a close second. Dund-Us is more centrally located in the zone, which might give it more of an edge. Yours, Gwillim Law