[Xastir] Re: Tons of Tiger Maps -- can we use them?

[Tom Russo]

On Tue, Nov 25, 2003 at 10:36:33AM -0600, a Mr. Richard Feyler of Fort Lee, New Jersey <gerry.creager at tamu.edu> writes 'Dear Rosanne Rosannadanna':
> Warning!  Warning Will Robinson!  Warning!  Datum error!
> 
> 300m in NM sounds like a NAD27/NAd83 offset.

Well, it almost does if taken out of context.  300m in my area exceeds the
normal datum shift which is at most 200m.  Plus I didn't actually say 
"all the streets are shifted" but rather "my street is shifted."  Fact is, 
the tiger map is just not accurate in my area.  Some streets line up perfectly, 
others bear no resemblance whatsoever to the streets whose names they bear --- 
mine is one, as it's not only shifted, but completely the wrong shape.  

Overlaying the tiger map on any other raster or line map of the area 
shows *some* agreement, but not consistent error or shifting.  The USGS and
USFS DLGs and CFFs of the same area line right up on top of the terraserver
photos of my area, but whether a tiger line will line up with a feature 
seems to be hit or miss.  Larger roads are mostly right, small dirt roads
are very, very wrong or completely accurate.  Their field-checker might have
been sampling the local mushrooms.

T.
-- 
Tom Russo    KM5VY   SAR502   DM64ux          http://www.swcp.com/~russo/
Tijeras, NM  QRPL#1592 K2#398  SOC#236 AHTB#1 http://www.qsl.net/~km5vy/
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