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[aprssig] Re: FindU Maps Quirky

Gerry Creager N5JXS gerry.creager at tamu.edu
Mon Feb 7 13:21:38 UTC 2005


Time's short, but I feel obligated to answer this.

The origin of a LOT of the maps we're using is the Census Bureau's 
TigerMap line files.  A lot of their data are derived from the USGS SDTS 
linefiles.

Recently I went through the xercise of determining the accuracy of 
TigerMap data with someone in the New York area.  Despite what I've been 
told over the years, regarding accuracy of the USGS maps... and what 
I've found of their accuracy... we eventually determined that Census 
munges these files with their own "data" to reflect what THEY need. 
What CENSUS needs includes tract data that may not be consistent with 
MAP data.  If one of their folks goes out and drives an area, 
hand-sketching a tract, and reflects in that drawing changes to roads, 
you may very well see changes to a TigerMap changed based on a sketch 
and NOT a more consistent method of mapping.

NIMA (now NGA) and USGS mean it when they claim to comply with National 
Map Accuracy Standards.  Apparently, Census does not, and since they're 
NOT a mapping agency, no one has called 'em on it.

Why should publc funds pay for TigerMaps?  Simple:  They're doing what 
Census needs, and that's what Census had 'em created for.

To put a point on it, Tiger is more a picture than a map.  The metadata 
associated with the Census info are "OK" probably, as that's what 
they're interested in, but for MAP use like we're doing, we've been 
going to the wrong well.

TigerMaps have been a convenient way to get what we thought were 
reliable maps for years.  We just did not do our due diligence.  It's 
OUR fault for using these maps imroperly, not theirs.  If you actually 
read their website, which I'd glossed over so long, you find the 
appropriate disclaimers.

What I guess I'm saying is, as USGS flies and updates (electronically) 
all their SDTS mapping resources, that's a good way to go.  If someone 
wanted to snag the SDTS data and turn 'em into shapefiles, and serve 
these out as shapes, and even rasters, that's a service to THIS 
community that'd be a good thing.  It's a service to a larger community 
that'd be appreciated, too.  USGS doesn't have the mission or resources 
to serve these data out like that, and if y'all are following the new 
budget the Prez is about to submit to Congress, I don't see Commerce 
(NOAA and USGS) getting more money in the next, oh, decade...

gerry

Ray McKnight wrote:
> Okay, so public funding provides the incentive to create these databases?
> If the results are so poor as to be basically unusable, then why should
> Public funds (we're talking specifically within the USA here) be 
> continued?  There are many other programs that are publicly funded, AND
> Result in enforcement by various government agencies if the user fails
> To comply - I'm referring to NIMA charts and commercial shipping, the
> Charts need (**MUST**) be accurate and the ships must navigate accurately
> According to those charts, if the ship doesn't there's heavy penalty
> For failing to navigate properly.  But if the charts are wrong, then the
> Ship can easily claim false navigational info was provided to them and
> Say they only followed what was required of them to use.
> 
> APRS certainly isn't such a high profile user of public data,
> Who cares if your house is shown 1 mile off an APRS map, or your car
> Is in the wrong lane of an interstate.  But if public funds provide the 
> Means for the data to be collected and provided to us, and it's
> Not sufficiently accurate as to be useful, then why continue to
> Fund its programs??
> 
> Make them accountable!!!!  ONE MILE+ ERROR IS REDICULOUS!!!
-- 
Gerry Creager -- gerry.creager at tamu.edu
Texas Mesonet -- AATLT, Texas A&M University	
Cell: 979.229.5301 Office: 979.458.4020 FAX: 979.847.8578
Page: 979.228.0173
Office: 903A Eller Bldg, TAMU, College Station, TX 77843




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