On Sun, 16 Oct 2011 12:44:41 +0100, Terry Pinnell
wrote:

[Snipping my original message]

Thanks both. That makes sense. In fact now that I think about it more
seriously it's sort of obvious that for a road some 130 miles long there
would have to be great provision for flexibility.

My assumption about 1 mile 'groups' proved wrong, as the 19000 to 20000 is
about 1.3 miles.

I haven't examined much more of the PCH's 131 miles, but the semi-random
pattern looks similar to the section I illustrated.

BTW, this has me wondering how properties in any country end up uniquely
numbered when many of them on the same road/street are built years apart?

In my road, a small housing 'estate' of maybe half a dozen building
types, all the numbers except one follow the simple pattern, 1 2, 3 etc.
I'm guessing they were all planned at the same time and building followed
the plan strictly. Or perhaps it started at one end and subsequent
development had to take place progressively on the next physical plot.
Otherwise you'd end up with numbers bearing no relation to position ion
the street.

I live in the suburbs of Los Angeles. In most of the urban area
comprising Los Angeles and other cities of the region, the numbers
basically run the entire width of the county area from the ocean on
the west and south to neighboring counties on the east, and are
divided into East and West and North and South. There are exceptions
in some cities, however--mostly larger or older ones that probably
preceded the establishment of the county-wide system. I happen to
live in a very small area that is inside Los Angeles county but,
because the development straddles the county line, takes its numbers
from adjoining Orange County.

The exception is our house, 29A. It was built later than the 3 similar
designs at numbers 25, 27 and 29. Probably on land that was either
originally part of a larger house's garden (yard), or that was initially
considered unsuitable.

Secondary homes on the same property may become A, B, C, etc. or,
more rarely, become xxx1/2.

I think the general scheme is widespread in the US, but not universal.
--
Don Kirkman