I wrote on Sunday that Portland, Ore., has been more successful than I might have guessed in promoting population growth. But it's still true that even inside the urban growth frontier, the area is—like most of America—hobbled by anti-density, anti-urban rules. Here above, for example, is the summary table of what you're allowed to do in those parts of the city of Portland that are zoned for multifamily dwellngs.
FAR is "floor-area ratio." Basically if you have a four-floor building that occupies 100 percent of a lot, you have an FAR of four—there's four times as much floor space as lot space. Four is a pretty high FAR for America. Christopher Leinberger says a neighborhood with a .8 FAR is generally walkable, and car-free lifestyles start being possible at around 1.5 (although note that neighborhood FAR will generally be lower than a building's FAR because you'll have parks and whatnot), so the maximum density is definitely "dense enough" for urbanism. But it's still clearly much less dense that modern engineering is capable of building.
That's a shame because the zoning document says "Generally, RX zones will be located near the center of the city where transit is readily available and where commercial and employment opportunities are nearby." The thing about locations "near the center of the city" and/or "where transit is readily available" is that there are pretty sharp logistical and fiscal limits to how many places like that you can create. To build anything less than the maximum amount of housing the market will bear in such scarce places is very sad.
And of course that's just the densest zone. Most of the multifamily territory is zoned for less density than that, some of the city is zoned for exclusively single-family homes, and in Portland—like all American cities—most of the land is in the suburbs where exclusionary zoning practices are generally more severe.