For the geographic domains, they used two letters, matching another international standard for coding country names. That's why many British companies are "co.uk" instead ".com," they've registered in the ".uk" geographical domain. Each country can handle what happens to the left of the dot as they see fit. The UK decided to replicate the top-level domains to some degree, using ".co.uk" instead of ".com.uk" for example.
Managing the three-letter domains was subcontracted out to a company called "Network Solutions," which ended up making them very rich before they lost their exclusive license to manage those domains. The .us domain, however, stayed with the Internet's governing body, the IANA. Specifically, the .us domain was managed by Jon Postel and Ann Cooper at USC. They decided to sub-divide the domain, and then delegate the registration duties.
Keeping with the geographic theme, they set up a subdomain for every state, based on its two letter abbreviation. Thus ".wa.us" for Washington, ".or.us" for Oregon, and so forth. Below that would be a city or county name. So, "seattle.wa.us" and "portland.or.us".
They went on to provide standardized codes for official governmental organizations. City government would be "ci" and county government would be "co". So, ci.seattle.wa.us would be reserved for the City of Seattle. The state government would be "state," as in state.wa.us or state.ca.us.
Makes all kinds of sense, doesn't it? If you want to load the web site of your local city government, you can just type in "www.ci.[yourcityhere].wa.us" and go there.
Did anybody ever do that? Absolutely! Try it! Try it with Seattle, Everett, Redmond, Chehalis, Walla Walla (you'll need a hyphen, as in 'walla-walla'), Federal Way (same thing), Blaine, Ellensburg, George, and many others. In many cases, you must include the "www" at the beginning, even though there's no technical reason to not also allow just "ci.seattle.wa.us" to work.
Postel and Cooper also reserved a space for schools, right down to elementary schools. "[schoolname].[schooldistrict].k12.wa.us"
Oh, yea, and unlike all those three-letter domains, these domains were free. Well, usually. Postel and Cooper didn't charge for registering or delegation, and it was generally understood that whoever would be handling the subdomains shouldn't charge more than a nominal fee for their registration work. Most companies that handled the subdomains also didn't charge.
So, waaaay back in 1998, I applied for and received the domain "howell.seattle.wa.us". I was actually living in Tukwila at the time, but who else in the country knows where that is?
So, would YOU like a free domain name like mine? Can you still get one? Well, that is a very good question. Eventually, Postel and Cooper realized they had better things to do than manage an unfashionable TLD, so the ".us" domain itself is now administered by NeuStar. Now, NeuStar will be happy to sell you "yournamehereifavailable.us", but their website has nothing about the geographic domain system, except for this oddly erroneous statement: "Formerly the exclusive online province of schools, libraries, states and branches of the federal government, the .US domain of today is the official country code top-level domain (ccTLD) for the United States, and is administered by Neustar." Yea, sure. (1) It was never exclusively for schools, libraries, et cetera, and (2) it has always been the official country code top-level domain for the US.
Further, NeuStar cannot sell you "[whateveryouwant].seattle.wa.us" because they don't have any control over "seattle.wa.us." The "seattle" subdomain belongs to Northwest Nexus. That's who I had to email my domain request form to way back in 1998. NWNexus has never, to my knowledge, had any information whatsoever on their web site about the fact that they're the designated registrar for the seattle.wa.us domain (and many other similar domains, like bellevue.wa.us and centralia.wa.us). I believe they still handle updating the seattle.wa.us domain information by hand, probably because they so rarely get anybody even trying it.
In fact, the whole geographic domain system is sadly neglected, and kind of falling apart, which is too bad, because I certainly think it's better than the alternative. If you enter "ci.ellensburg.wa.us" into your browser, you get to go to Ellensburg's official page. The same is true for Portland, but your browser will first be redirected to an alternative domain that they seem to think is better: "portlandonline.com" What? Well, guess what. "Portland.com" already belongs to somebody else; some corporation in Portland, Oregon. If you try "ci.auburn.wa.us" you get the City of Auburn's web site, but with a "file not found" error. Oops, they forgot to have . . . a home page? What???? You can't even get to their real home page from that page, which is "auburnwa.gov". If you try to visit "www.ci.federal-way.wa.us" you'll be sent to "cityoffederalway.com". Same for Chehalis.
Anacortes is even more mysterious, since going there presents the message "You have arrived at this site because the US Locality domain you are searching for has been given back to Neustar Registry to manage." Anacortes.wa.us wasn't assigned to NWNexus, it was the responsibility of some outfit called "nametamer." Guess they went under or something. The domain name "nametamer.com" now belongs to a company in Troy, NY, but they don't have a web server responding to it, and the name record says it was created in 1996, so the current name owner may have no relation whatsoever to the company that was responsible for anacortes.wa.us.
It's actually kind of scary that this whole system of domain naming, which is clearly still widely deployed, has, in effect, vanished from the Web. Even Wikipedia is nearly mute on the topic; there's a small article about the ".us" domain which mentions in passing that only US citizens or companies can use it, but almost nothing on how one might go about doing so. NeuStar's site is also very terse and quite vague. Even though I know exactly what I'm looking for, I haven't been able to find any other information about these domains. I would never have imagined that the World Wide Web could so completely "forget" about such a gigantic component of its own being.
I'm glad I'm not the kind of guy who believes in conspiracy theories.