Where are address numbers made from?

[cpzilliacus]

In Montgomery County, MD, the unincorporated areas and most of the smaller municipalities (i.e., most of the county) base their numbering system roughly on DC's, which is roughly a Cartesian grid with its origin at the Capitol.  It thus makes sense that in the subdivision where I grew up, numbers began with 4800 on east-west streets and 10900 on north-south streets.

Kensington or Garrett Park, perhaps?

To add to the fun, since the (virtual) boundary between Northwest and Northeast Washington extends north into Montgomery County, the east-west streets come down to unit blocks in the eastern part of the county.  Hence Md. 193 is University Boulevard West on the west side of U.S. 29, and University Boulevard East on the east side of 29 (I grew up near there).  Same thing happens in Prince George's County, though there the boundary is between Northeast Washington and Southeast Washington, and the boundary is reasonably well-defined by Central Avenue and East Capitol Street (Md. 214).

[getemngo]

How is it decided which side of the street will be even or odd addresses?

...

In a grid system, if your origin is in the middle of the road, typically your north and west sides of the street will have odd numbers.

How universal is this, really? In my county, the south side of the street is odd.

[spooky]

I've heard it said that the odd numbers will be on your right if the numbers are increasing as you travel down the street, which I've since found to be only mostly true here in New England.

[Brandon]

In a grid system, if your origin is in the middle of the road, typically your north and west sides of the street will have odd numbers.

Not always though.  This varies quite considerably from municipality to municipality.  It can also cause some confusion where two municipalities with differing even/odd systems meet.  Here's an example in Illinois:

Around Chicago, odds are commonly on the west and south sides of the street with evens on the east and north sides; however, a few municipalities around here do things differently.  Joliet has odds on the north and west, neighboring Crest Hill has odds on the south and west.  They share a street, Theodore Street (IL-7) between them.  Now, as Joliet uses evens on the south side of a street, and Crest Hill uses evens on the north side of the street, all addresses along Theodore are even from Broadway (IL-53) to the Joliet Junction Trail (former EJ&E RR line).  There are no odd addresses along Theodore during that stretch.  Fortunately, there are few potential conflicting addresses.

[kkt]

King County's is based entirely on Seattle's road numbering system, which continues to the rest of the county.

If you lived just north of NE 47th St on 17th Ave NE, then your address would be 47XX 17th Ave NE.  If you lived just west of that intersection on 47th St, your address would be 16XX NE 47th St.  It makes it pretty damn easy to find where you need to go.  You can literally look at the address and know immediately where it is geographically.  You just have to know where NE changes to N or NW, etc.

I'm pretty sure most counties with numbered roads do this.   

Except the city of Auburn has its own numbering grid, surrounded by King County's grid.

Seattle's is only easy once you're in the right general area.  It's easy to think you're near the right spot and then discover that you're in East streets instead of East streets and avenues.  The worst of the peculiarities are not continued into King County.

The King County grid typically goes up by 2000 house numbers per mile.  It is a dense grid, to allow flag lots, small apartment houses, etc., to each have their own house number.

[Road Hog]

The county I used to live in went to a 911 system about 20 years ago. All addresses outside the county seat and one other town went to a system where 1000 = 1 mile. My house was 704, meaning 0.704 miles from where the road began. There wasn't any odd/even left/right split as far as I remember.

(fixed misplaced decimal point)

[ibagli]

Coshocton County, Ohio uses a grid with about a thousand numbers to the mile, but the origin is somewhere else entirely, and I'm not sure why. The range is 31000-61000 from west to east and 14000-34000 from south to north. Estimating it with Google Earth's ruler, the origin looks to be in eastern Franklin County, somewhere around Reynoldsburg.

Edit: I think it was to match up with Knox County to the west and Muskingum County to the south. So one baseline is the western edge of Knox County, and the other is somewhere in the middle of Muskingum County.

[brownpelican]

In New Orleans, the grid is based off the old French Quarter. Canal Street is the dividing line between areas upriver and downriver and starts at 100 and increase by 100 per block, as the grid mainly follows the Mississippi River. Most streets closer to the river are marked North and South; however, addresses going downriver are marked North while addresses going upriver are marked South. Also, address numbers go up from the river to Lake Pontchartrain. From Canal Street, the address numbers continues to increase through New Orleans East.