In search, Emerald City came up with a number of hits, which condensed into two actual places. The one with the actual sim name is a camping/casino/shops/neko-friendly danceclub area, which does have the redeeming features of a few amusement park rides, and popcorn! It's also very movie based, not surprisingly. (I prefer the books.) It's a neat place to see though, and all the camping not in the casino is "work for your pennies" floor mopping, gardening, etc. which is kind of cute with the Emerald Citizen tags over everyone's heads (I have one of those tags. I actually kept it because I like it, for personal reasons). There are 2 sims diagonal to it, the Scarecrow Fields is currently an empty expanse, and for sale, but the Tinman Forest has a little cabin by the water, and a forest area in the middle with poseballs and all sorts of stuff related to that scene in the movie. I go there to be alone sometimes (not as though you can't go almost anywhere in SL to be alone). If I knew a bunch of people in SL, if I were actually a social person and didn't generally actively avoid people, I would love to have a group where we found strange little deserted areas and just descended en masse to hang out. There's a great little pirate cove I found somewhere (I shall have to see if I can figure out where it was sometime) that would be great for it too, even if it does back onto a mall (you wouldn't know if not for the minimap and flight- there's a nice rock wall between you and it).
The other Emerald City was the one I was looking for- I've joined SL Deathrock and was browsing through other like minded groups, and found mention of someone's shop in Emerald City. Turns out that one is in Big Star (and used to be in Lonsdale? I don't know my SL history), and is a goth/punk hangout, with shops and a nice little hole in the wall club (and sky apartments, I believe. I haven't made a flight assist to be a nosy Nellie yet). The shop area is a bit confusing to make one's way around, but then, they often are with the booth system. It has cute graffiti'd walls around the outside, which I rather like (and even though I'm sure they are repetitive, I didn't really notice). And they share the sim with some Gorean, who has a castle over the mountains, a nasty attitude towards "trespassers," and has turned fly off so once you get there you can't get back out. I was finally able to edge enough out into the river before it got too steep to be able to get out, but really, making it so people can get in and not get out is not the way to make people not crash your pad.