I like 13th as the northern border because it's a clear delineation between downtown and the residential area of Mesta Park / Heritage Hills. Almost everything between 13th & 23rd is single-family.

There are some exceptions but then why not take it to 23rd and beyond? Lots of multi-family in Jefferson Park and the Paseo; tons of 8-plexes and the like.

When I think of downtown, it seems that includes the CBD, Film Row, SoSa, Midtown, Bricktown, Lower Bricktown, Auto Alley, Deep Deuce, Flatiron and Core to Shore. And Midtown definitely stops at 13th street.

You do have Uptown/23rd, The Plaza, Heritage Hills, Mesta Park, Gatewood, Classen-Ten-Penn and a bunch of other urban districts, but I wouldn't include them in downtown.