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[aprssig] Re: FindU Maps Quirky

Bill Diaz william.diaz at comcast.net
Mon Feb 7 13:41:43 UTC 2005


Steve,
  See below regarding PMap errors in the Michigan's upper peninsula.

>-----Original Message-----
>From: aprssig-bounces at lists.tapr.org 
>[mailto:aprssig-bounces at lists.tapr.org] On Behalf Of Stephen H. Smith
>Sent: Monday, February 07, 2005 02:53
>To: TAPR APRS Mailing List
>Subject: [aprssig] Re: FindU Maps Quirky
>

>
>Ray McKnight wrote on 2/6/2005, 11:21 PM:
>
> > Steve, if you zoom in to street level on my FindU map,
> >
> > You'll notice that although I am actually located about 1 mile
> >
> > From the water, a significant amount of the streets in my 
>neighborhood
> >
> > Are depicted as being in Puget Sound, yeah, in the water!
SNIP

>The real issue is how much do you want to <<PAY>> to have access to 
>commercially enhanced and corrected data versus using free 
>public domain 
>  data???

Commerical products, such as Precision Mapping use map databases from
multiple vendors and sources including the Census Bureau.  The commercial
vendors add value to the data by integrating the different sources into one
map.  Map registration differences are common and can be time consuming to
resolve.  Not unusual for some errors to be missed due to the huge volume of
data required to draw every street in the US.  See below.

The accuracy and completeness of street data is entirely dependant on local
governement sources.  The Census Bureau and other federal agencies in most
cases aggregate (and in some cases correct) data provided by these sources
into publicly available map databases.  Local governements do not always
provide the needed data (new subdivisions, streets etc) or they provide
inaccurate data. Errors abound, and are often not corrected in the
aggregated databases due to the huge volume of data. If you find
inaccuracies in street data in your area, it is likely your municipal or
county government is to blame.  Map vendors cannot be expected to correct
errors in individual streets due the high percentage of inacurrate or
incomplete data.  Also, if you submit a correction to a map vendor, how do
they verify the accuracy of your submission?  It is impractical for them to
verify street data with every municipality and county government in the US
and Canada.

>Note:  You can see some similar errors in Precision Mapping 7.0   
>Zoom in on the channel between the eastern tip of Michigan's Upper 
>Peninsula and Sault Ste Marie, Ontario.   You will see Canadian 
roads, including >Ontario Route 548 apparently in the water, along 
>with a bunch of small towns.  Somehow the outline of an entire 
>island (St Joseph's) slipped through the cracks of the Canadian 
>database provided to Undertow 
>software by GDT (Geographic Data Technology).
>

We noticed the same (and more) errors during the development of PMapServer7
for Ui-View. For example, islands in Thunder Bay, ON were in the water and
water polygons around various islands elsewhere were not painting correctly.
I notified Undertow and they provided a correction within about 2 weeks
which fixed 99% of the observed problems.  One exception can be seen in the
St.Lawrence river but I am told it is unrelated to the original complaint
and involves some incompatibilites between the GDT Canadian and US data.  In
any case I think Undertow has included the corrected file (MHydro.Zpx, about
19MB) in newer releases. The original MHydro file was about 8 or 9MB as far
as I can recall. I don't think the new file is availble for download from
Undertow.  Perhaps someone with enough bandwidth can host this for download?

We also complained about misspellings of some islands in the Pacific.
Palmyra Atoll was the most glaring example since it can be seen when zoomed
out to show the world. Undertow had to manually edit the vendor supplied
database to change Palynyra Atoll to Palmyra Atoll.  If your map shows the
incorrect spelling registered users can get the newer and corrected version
by downloading and installing the latest version of the Precision Mapping
and Traveler 7 from http://www.undertowsoftware.com

The average user complaint is unlikely to get resolved if it is considered
relatively minor and requires considerable time to resolve.  Fortunately,
Undertow has shown support of the APRS community over the years and was
willing to expend considerable effort to resolve issues which would affect
APRS users.  The impending release of PMapServer7 (and additional PMap
sales) was certainly a factor in Undertow's willingness to make the
corrections in a timely manner.  Don't expect similar action for what they
consider to be minor issues.

Bill KC9XG

Bill KC9XG
>
>
>Stephen H. Smith                wa8lmf (at) aol.com
>





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