[GRASSLIST:3081] Re: TIGER/Line Data

[Ben Logan]

On Sun, Feb 03, 2002 at 01:30:33PM -0700, Roger Miller wrote:
> On Sunday 03 February 2002 12:50, you wrote:
> 
> > Does GRASS support the TIGER/Line data format used by the Census
> > Bureau?  I looked on the GRASS homepage, but couldn't find anything
> > about it.
> 
> I did this recently with Tiger 2K county data.  I used v.in.tig.basic.  I got 
> the lines themselves, but I didn't get the topology or the attributes.

Ok, thanks.  I also see v.in.tig.lndmk.

In the v.in.tig.basic manpage, it says you have to specify the
spheroid to use.  I've read a lot on the TIGER info page, but can't
find anything about a spheroid.  On one of the pages[1] it says the
following:

"In the 1995 and later TIGER/Line® files, NAD83 is the coordinate
datum used for the 48 contiguous states, the District of Columbia,
Alaska, Puerto Rico, and the Virgin Islands of the United States."

And later on

"The TIGER/Line data are not in a mapping projection even though most
of the features were scanned directly from source maps (usually USGS
1:100,000-scale topographic quads) that were in a projection.

"For the lower 48 states, most information in TIGER outside the urban
centers was derived from the USGS 1:100,000-scale digital line graphs,
which were vectorized from the digital scanning of the original
artwork.  The original art work was in Universal Transverse Mercator
(UTM) projection.  After the map sheets were scanned, the coordinates
were transformed from UTM into projectionless geographic coordinates
of latitude and longitude."

Looking in $GISBASE/etc/datum.table, I see that NAD83 uses the grs80
spheroid.  Whenever asked by something, is that the spheroid I should
use?  (Sorry for the elementary questions, but I'm new to this and
want to be sure to get it right. :)

I think I would like to create a new GRASS location for this data.
However, I don't know the extent of the data (the geographic region)
before importing it, and this seem to create a kind of chicken and egg
problem.  How do I go about doing this?

I hope I've made myself clear.  Thanks for your help,
Ben

[1] http://www.census.gov/geo/www/tlmetadata/metadata.html

-- 
Ben Logan: ben at wblogan dot net
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Q:	How was Thomas J. Watson buried?
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