When my dad was here for Thanksgiving he commented on once getting lost near my brother's apartment in West Seattle because he thought that California Ave SW would intersect the numbered avenues, not being itself a numbered avenue. I had to point out to him that in Seattle there are both numbered streets running east-west and numbered avenues running north-south, like in Manhattan (technically this is true in Chicago as well, but usually it can be ignored), and that generally there are both named and numbered streets running every which way. Unlike Manhattan, there are eight “quadrants” to Seattle's address and street grid (maybe nine, more on that later, although only six of them are distinct as far as addressing is concerned, and two of them overlap). Another difference with Manhattan: Manhattan has a Nexus of the Universe at First and First, and Seattle would never be so presumptuous as to claim one of those, right?
I wondered about that while out running today. As Seattle has many quadrants, it could potentially be a Universe with several nexi. That would suit Seattle just fine. As I was out running I had no map and plenty of time on my hands. The following is how I reasoned about this.
The central quadrant has numbered avenues but no numbered streets; or if it does, they're not close to 1st avenue.
I don't think the North, East, or West grids have any numbered streets either, but I'm not totally sure about that. I called those doubtful.
The Northeast and Northwest quadrants share an origin with the East and West quadrants respectively, so though they have both numbered streets and avenues, neither extends far enough south to have a 1st Street.
I'm not all that familiar with the South quadrant; I think it has both numbered streets and avenues, and it certainly has a 1st Avenue, but I don't think it has a 1st Street, at least as far west as 1st Avenue. I called the South quadrant possible but unlikely.
The Southwest quadrant has no land far enough north to have a 1st Street.
Then there's Southeast. I thought there was no Southeast quadrant, but my brother's girlfriend's uncle Fred says there is one, and he would know better than I would. My guess is that it exists nowhere within the city limits of Seattle, perhaps only on the Eastside, and shares an origin with the South quadrant, and thus doesn't extend far enough west to have a 1st Avenue.
I checked a map after getting back, and found a few interesting things. Indeed, there are no numbered streets in the Central, North, East, or West quadrants. There is, oddly enough, an E Fir St right where you'd expect E First St to be (I did a double-take there), but the East quadrant doesn't go far enough west to have a 1st Ave, and Fir St, by virtue of its location and the twistiness of the grid in that area, never appears in the Central quadrant. The South quadrant, as far as I can see, has no numbered streets until you get quite far south.
There is a SE quadrant on the Eastside, and the Eastside also dispenses with the silliness of the E quadrant entirely, so both the NE and SE quadrants have a 1st Street over there. Neither have anything near a 1st Avenue, of course. Bellevue takes the additional rationalizing step of having a “zero street”, called Main Street. It also takes the irrationalizing step of having NE 1st St run diagonally, so it eventually intersects NE 10th St. Some towns on the Eastside have their own grids. Kirkland is an example, and it appears to have Central, West, and South quadrants. Each comes tantalizingly close to a First and First that never materializes. EDIT: Kirkland, unlike the rest of the region, has numbered streets running north-south and avenues east-west, except in the diagonal west part of the grid. Another example is Renton, which has east-west numbered streets but not numbered avenues.
As for other counties, Snohomish has a nice grid system, but its “nexus” would fall in the middle of the water. Pierce County's grid looks to be based on Tacoma, which is possibly even weirder than Seattle, and as far as I can tell doesn't have a “nexus” either.
So... I could be wrong, but I don't think there's a Nexus of the Universe anywhere near Seattle.
ADDENDUM: As for Chicago, I think the lowest numbered street is 8th, and the lowest numbered avenue on the main grid is somewhere in the 40th. There's a 1st Ave on a different grid system that runs through parts of the west suburbs, but no numbered streets on it. So there's definitely no “nexus” in or around Chicago. And Seattle, Chicago, and Manhattan notwithstanding, the real Nexus of the Universe is at Main St and Center Ave in the middle of North Dakota. Some day I want to bike there for some reason (I don't know if the roads are paved... details, details...). Also, the statewide North Dakota grid has three of the four possible 1st-and-1st intersections intact, which is cool.