Nearly every data set that is commercially sold has various levels of
copyright protection.  The intentionally introduced 'errors' typically
have no effect on the data usage, though (otherwise it wouldn't be useful).

An error might be a straight road could be represented by one line
segment, but is instead represented by several shorter segments.  The
lengths of the segments may even represent binary data.

The may contain minute road variations (ie, a number in a road segment
may have 12 significant digits, but the measurement is 'too accurate',
they never could/would have measured it to the micron)

There are other methods.  Obviously the above watermarks could be
removed with a suitably advanced vector optimization program.  They are
mainly trying to keep others from profiting from the data set without a
license, so someone taking the data, changing it to another (perhaps
proprietary) format, then selling it with or without a viewer.  All they
need to do to prove copyright in court is say "view the following
lat/long coordinates at such and such a resolution - it should exactly
match this output of our own software, but the features are artificial"

Programmers do the same thing with programs, and there are likely even
PICs out there that have watermarks on them for the same reason.

-Adam

Josh Koffman wrote:

>Be careful if you use these though. I seem to remember hearing that the
>USGS (United States Geological Survey) used to put intentional errors in
>their maps so that if someone used them without paying royalties, they
>had evidence and could take them to court. I suppose if you paid the
>requisite fees, they gave you the corrections.
>
>Josh
>--
>A common mistake that people make when trying to design something
>completely foolproof is to underestimate the ingenuity of complete
>fools.
>        -Douglas Adams
>
>Jim wrote:
>
>
>>   "Where do all the companies like Delorme, Mapquest, &
>>    Magellen get their database?"
>>
>>>From digitized USGS 7 1/5 minute topo quads (24,000:1 scale
>>topographical quadrangle maps)?
>>
>>
>
>--
>http://www.piclist.com#nomail Going offline? Don't AutoReply us!
>email listserv@mitvma.mit.edu with SET PICList DIGEST in the body
>
>
>
>
>
>
>

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listserv@mitvma.mit.edu with SET PICList DIGEST in the body