[postgis-users] Greetings, and road data questions
explorer at flame.org
Fri Oct 18 11:49:07 PDT 2002
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I'm new to the postgis thing, but am working on a spare-time project
dealing with maps and such.
I have all the tiger/line data loaded into tables using some fairly
primitive schema. The overall data set of line data consists of
nearly 14 GB and 46,701,436 rows. There are some duplicate tlids in
there, since the tiger/line data is organized on county boundries.
This is probably the largest dataset I've worked on that wasn't
faked-up test data.
I have a Perl map generating toy that makes maps in whatever detail
desired, given a center point and a block size. The database works
amazingly well for small values, but gets rather slow rather quickly,
even with filtering out unwanted rows using the SQL query:
SELECT cfcc, path FROM cp WHERE path && <box definition>
AND (cfcc LIKE 'A1_' OR cfcc LIKE 'A2_' ...)
My next plan is to split the waterways, railways, and roads into their
The ultimate plan will probably involve generating ploygon information
from the files and combining many short road segments into one longer
one, for all the A1, A2, and A3 road types.
And yes, I know I could use mapserver for this, but I sort of like
So, the questions are:
(1) How are others using the tiger/line data? Are they mostly doing
what I plan, or is there an easier way that I'm overlooking?
(2) Garmin and others have fairly detailed maps, both as a windoze
application and as a GPS product. Where do they get their data?
(3) I know of USGS sources of data (the infamous DLG files) -- are
they more or less correct than the tiger/line data? How about
ease of use?
(4) If you wanted to write a mapping application that would track
multiple objects and show both an overview map of where they are,
and detailed maps for each, would you use tiger/line or DLG, or
something entirely different?
(5) Are there sources of other street data available, such as for
Mexico, Canada, and other countries? If this project of mine
becomes a product, I'd be interested in avoiding remaining too
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