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    Re: fire & police department navigation
    From: Jared Sherman
    Date: 2004 Jul 20, 18:50 -0400

    Fred, basic 911 systems often didn't have caller-ID, the new ones are
    generally called enhanced 911 (e911) and include it. The FCC and the telcos
    are playing with cellular tracking and while there was a big push for GPS in
    the phones, that of course is useless whenever there is no skyview. Like in
    buildings, parking garages, or locked in the trunk with your phone as people
    have been. The competing technology is actually just radio direction finding
    (RDF) using the timing from a phone to the three nearest towers that can
    capture it's signal. Obviously, this requires you to be in range of three
    towers. In rural areas, they only get a distance out from one or two towers
    and have to do more work.
    The RDF scheme requires new equipment in some systems, but only a software
    upgrade in many of them, so it looks like that will be the market leader
    here. The few companies hyping agreements about gps in phones (like Benefon
    (sp?)) seem hard pressed when you actually ask them "Where can I buy one,
    and get full service on it, now?"
    The prime sources for road data in the US are the state planimetric maps,
    normally available at any repository library for that state, which are made
    and keep up by state authorities for tax and other purposes. That's "the
    word of god" to a cartographer here today, even though they will contain
    errors and omissions--which some cartographers also intentionally insert to
    track copyright.
    The other prime source is the US Census Dept. "Tiger" maps. I'm not sure how
    those are created but suspect it is a combination of the USGS mapping and
    the state planimetrics. The Tiger maps are available free in electronic
    format for the entire US, and there are commercial products to read them,
    some very inexpensively.
    The big map publishers here these days don't seem to take much pride in
    accuracy or updates, I think they're just pursuing the market and assuming
    the government maps are good enough.

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