[postgis-users] Greetings, and road data questions

[Roger Bedell]

Michael,
I've been doing this a long time (not PostGIS, but for AutoCAD, SHP, DGN
etc), and here are some observations:

(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?

I split it into smaller pieces, but that was more useful before PostGIS.
Today, I'd do it like you plan.

(2)  Garmin and others have fairly detailed maps, both as a windoze
     application and as a GPS product.  Where do they get their data?

Probably either TIGER, or a private deal like GDT, NavTech, Teleatlas.

(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?

DLG files have very limited attributes, like no road names. The 100K DLG
files were the basis of TIGER in rural areas. TIGER uses the lame DIME
files in urban areas, very inaccurate center lines.

The 24K DLGs are quite accurate, but old. Also, only about 40% coverage
of the US.

(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?

You could split out the major roads from TIGER, that works ok - see
www.sylvanmaps.net/dbs/dbs.asp (this is not an ad, just an
illustration).

(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
     US-centric.

Right - possibly Canada, possibly the UK, but otherwise it's pretty bad.

Roger Bedell, President, Sylvan Ascent Inc.
roger at sylvanmaps.com
www.sylvanmaps.com
www.topodepot.com
505-758-7712


-----Original Message-----
From: postgis-users-admin at postgis.refractions.net
[mailto:postgis-users-admin at postgis.refractions.net] On Behalf Of
Michael Graff
Sent: Friday, October 18, 2002 12:49 PM
To: postgis-users at postgis.refractions.net
Subject: [postgis-users] Greetings, and road data questions

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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
own tables.

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
hacking.

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
     US-centric.

Thanks,

- --Michael
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