I noticed something during a walk with my wife and son. Our neighborhood, which is only six years old, is filled with five-digit addresses. Another fairly new neighborhood nearby uses single- and double-digit addresses. What gives?

Paul Kalomiris, Germantown

I was recently putting together a database for a high school band reunion. While entering the addresses I noticed that out of 131 addresses, 106 started with either a 3 or a 6. The vast majority of the addresses were in Northern Virginia, specifically Falls Church. Is there a reason for that, or is it just a coincidence?

Michele Bach-Hansen, Centreville

In the case of these two queries, the first question we must ask is this: How are addresses created, anyway? Do a mommy house and a daddy house love each other very much and then when there's a baby house, do they give it a number?

In a word, no.

Storks don't bring new houses, developers do. And while developers may pick the names of the streets for their new subdivisions -- all of those "Foxchase Views" and "Lakespring Terraces" -- they don't pick the numbers.

The numbers are picked by people such as Lawrence "Lonnie" Rorie, whom Answer Man visited last week at the Maryland-National Capital Park and Planning Commission headquarters in Silver Spring.

What you should know about housing numbers is that there's a system. Without a system, you would be in bedlam. (Or you would be in England. Answer Man has an aunt there who once lived in a house with the street address "The Cottage." That's it: The Cottage. Of course, what do you expect from a country that names its town things like Chipping Sodbury and Leighton Buzzard?)

The basic method for determining what an address will be in Washington's close-in suburbs is the grid. Where the house is on the grid determines what number the address should start with.

Montgomery County is in the midst of automating this process. Until then, it's done manually. Lonnie and his staff consult massive books of bound maps, each one printed on sturdy linen. The corner of each page has a number representing the "coordinate value" for that part of the county. Lonnie looks up the coordinate value in a fraying notebook labeled "Block Number Relativity Tables."

The system is based on what's called the WSSC grid, in which a new hundred block starts roughly every 600 feet.

The grid in Montgomery County operates like the one in the District, where the digits increase the farther you get from the U.S. Capitol. (That's not the case in Howard, where addresses go up the farther you get from Baltimore, the original mother ship for that county.)

Same thing in Fairfax County, said Michael Freund in the county's Land Development Services division. The grid dictates that addresses start with the 1000 block in the northeastern corner of the county, then increase going west -- to the 16000 block -- and to the south -- to about the 12000 block.

There's a bit of finesse involved. Development doesn't march steadily across the landscape. It flares up here and there. Should a subdivision in the middle of nowhere start with 12000 or with 13000? What if something is built nearby later?

"We look at the county as one big puzzle," Lonnie said. "You just have to see where the pieces fall."

And they have to anticipate something else: Is it possible to carve up a property? If so, they try to leave some spare numbers. At Park and Planning, Lonnie had one page of his frayed, linen map book open to a new street called Fountain Drive. Addresses on the odd-numbered side of the street went 12401, 12405, 12409 and so on. The lots were big enough to be subdivided at some time in the future.

So what about our two questions? Why would some houses have five-digit addresses and others have one- or two-digit numbers?

The overarching factor in addressing houses is making sure they're easy to find.

"At two in the morning, if you've got a problem, you want fire and rescue to get there with as little trouble as possible," Lonnie said.

If similarly named streets are close to one another, the numbers will be adjusted. For example, imagine that the cul-de-sacs Briarpatch Court and Briarpatch Terrace are off a through street named Briarpatch Drive.

The all-knowing grid says that addresses in this area should be in the 17000 range. But if you had jotted "17102 Briarpatch" on a scrap of paper, you'd be lost in a hurry. Therefore, Lonnie might number the houses on Briarpatch Court 1, 3, 5, etc., those on Briarpatch Terrace 101, 103, 105, etc., and those on Briarpatch Drive 17101, 17103, 17105, etc. The number of digits would be a clue to help you keep your Briarpatches straight.

The grid is the explanation for the numerical synchronicity Michele noticed. Reston, Centreville, Chantilly and Falls Church all fall roughly within the same grids, said Michael Freund, the ones that dictate addresses start in the 6000 or 3000 range.

What if you don't like your address? Some Asian cultures consider the number 4 inauspicious. Other people might not be crazy about living at 666 Spawn of Satan Way or 1313 Broken Leg Parkway.

If the new number falls in the grid and it won't mess up the rest of the street, you might be able to get it changed. If there's already a 664 Spawn of Satan Way and a 668 Spawn of Satan Way, you're out of luck.

Answer Man wouldn't be Answer Man if he didn't have questions. Reach him at answerman@washpost.com or John Kelly, 1150 15th St. NW, Washington, D.C. 20071.