mod parent up. The way urban growth boundaries in Oregon work is that subdivision of parcels of land below some arbitrarily large size (I think it's 80 acres) is simply not allowed outside of the UGB.* The reasoning was that the UGB would allow farmers in the Willamette valley to continue their modest agricultural lifestyles without fighting against property speculators hoping to turn all of I-5 between Portland and Eugene into a soul-destroying chain of strip malls and burbclaves. And so far it's worked pretty well to achieve that purpose- while Eugene/Springfield is reasonably dense, there is literally NOTHING but sheep farms and hops vines in the 60 miles or so between Salem and Eugene.
The land speculation game is confined to the outskirts of existing cities- speculators can buy a big, relatively cheap parcel just outside the current UGB and hope that in 20 years, the city grows enough that at least some of their property will be pulled in, so they can break it into smaller lots and sell it. What the UGB has done is make it practically impossible for a speculator to buy a farm out in the middle of nowhere, bulldoze it flat, and build 100 houses on it... and that's just fine with most of the folks who live here.
Anyone who cares can read more here (html thanks to google)
*Local jurisdictions are allowed to make exceptions for various reasons, but "multi-unit housing development" isn't one of the allowed reasons. And of course all of the existing lots and structures were grandfathered in - the statewide UGB law was passed only about 30 years ago- much of the privately-owned land in particularly desirable locations (e.g. along the banks of the McKenzie River) was subdivided and developed long before the UGB took effect.
