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    Re: fire & police department navigation
    From: Fred Hebard
    Date: 2004 Jul 20, 17:03 -0400

    Our rural, mountainous county in Virginia went to what they call "911"
    addressing about 4-6 years ago.  There is now a street name and number
    for every street and house, and street signs have been installed on all
    the roads, including private roads (driveways with more than one
    house).  The post office switched to using this new addressing scheme,
    which enables most people to learn their "911" address.  The fire
    departments, ambulance services and police agencies are provided with
    complete, indexed street maps that also show the house numbers by grid.
      "Central dispatch," who receives the calls, provides the address to
    the appropriate responder.  (For those not in the U.S., if you have
    need of emergency assistance for ambulance, fire or police, dialing 911
    on your telephone connects you with "central dispatch").  I believe the
    address of land-line phones comes up on "central dispatch's" screen
    when they receive a 911 call; cellular phones also are being tied into
    this system, I believe, based on the cell they are in; there is talk of
    tying a GPS unit in the phones into the system.
    I had occasion to use the 911 maps a few years ago, and they were
    remarkably accurate.  A few times, street names changed inexplicably or
    street numbers did not increment the way one would expect, but that's
    to be expected with land maps.  I estimate our 911 maps show about 1
    mile per 4 inches, although this is a guess as I can't locate them
    I don't know whether the fire departments also have maps for adjacent
    I believe this was paid for by the Federal Government.  It also
    occurred in Kentucky before I moved here; it was aggravating having my
    street address changed without moving the house!
    On Jul 20, 2004, at 4:14 PM, Paul Hirose wrote:
    > George Huxtable wrote:
    >> The trouble with many road atlases is in their gridding. In many
    >> cases, the
    >> grid markings relate only to each map-page and are unrelated to the
    >> gridding of adjacent map-pages and bear no relation to a national
    >> coordinate system or to latitude or longitude or WGS84. So there's no
    >> way
    >> to relate them to coordinates taken from a GPS receiver.
    > Based on what I've heard on my scanner, the Los Angeles County Fire
    > Department "coordinate system" consists of the map page and grid
    > square from the Thomas Brothers road atlas! On the other hand, Kern
    > County Fire uses the township and section number from the U.S. public
    > land survey system. Neither system is usable with common GPS
    > receivers.

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