On a forum I follow, someone posted the ranking of large metros by urban density based on recently released ACS data. Portland was #10. Top 10 are as follows:
SF @ 7,626 ppsm
LA @ 7,476 ppsm
SJ @ 6,436 ppsm
NYC @ 5,981 ppsm
Vegas @ 5,046 ppsm
Miami @ 4,885
San Diego @ 4,550
Denver @ 4,168
Sacramento @ 4,163
Portland @ 4,052