shrug-l: Outside the Box Thinking

Sykes, John John.Sykes at
Mon Jan 7 16:53:14 EST 2008

Here's some food for thought:


My experience shows that the school location information in available GIS
layers leaves a lot to be desired (I recently plotted some schools in Volusia
County only to notice that they weren't even on the correct side of I-95!).


The only county that I know of that has address information posted for public
GIS use is Brevard County.  All counties are suppose to be putting this
information together for their 911/Homeland Security needs, but I don't know
how many of them are done and, again, the only one I know of that is publicly
available is Brevard County.


Recent widespread availability of high-resolution digital aerial photos has
shown that many county's parcel (cadastral) data is very inaccurate when
compared to other layers (assuming the other layers have some degree of know
accuracy).  New digital aerials are as good as +/- 3 ft, although they
usually only promise +/- 7 ft horizontal accuracy.


Finally, as I have already found, much of the GIS information out there is
based on 1:100,000 or, if you are lucky, 1:24,000 USGS topographic maps.  The
inherent accuracy for these maps are in the +/- 125 ft range at best - not
adequate for situations where the distance has legal implications.


Even "survey accuracy" data only is accurate to 1 part in 10,000.  Which
means that a 1 foot error over a 2 mile distance is acceptable.  We recently
did some GIS work with survey data from two surveys in Pensacola, the errors
were upward of 1-1/2 ft.


There are other reasons why I have already determined that trying to do
precision work in a GIS environment can be an exercise in futility unless you
obtain and QA all the critical information yourself and determine what an
acceptable error is.


-- John 


From: shrug-l-bounces at
[mailto:shrug-l-bounces at] On Behalf Of Sandell, Keith M.
Sent: Monday, January 07, 2008 4:22 PM
To: shrug-l at
Subject: shrug-l: Outside the Box Thinking


During recent months the Florida Department of Corrections began developing a
web based GIS solution for internal use to identify the residential
restrictions required by certain statutes and ordinances related to sexual
offenders and predators i.e. cannot live within 1000ft of a school, daycare,
etc. Our project encompasses the full extents of Florida with detail down to
all property parcels, which are the basis for many restriction measurements,
i.e. distances must be measured from property line to property line. A key
component to this solution is the ability to accurately and efficiently
locate any parcel within the state utilizing a search function. 


Many of the parcels in the metro areas of Florida have physical site address
attribute information associated which is helpful, so long as it is accurate;
however, many parcels, especially in rural areas do not yet have any physical
site address attribute information available, which can make it difficult, if
not impossible to accurately and efficiently locate 1 parcel within 9


I have given long and hard thought to many possible solutions and iterations
of those; yet I have a feeling that there is/are some solution(s) I am
overlooking. I need a fresh pair of eyes to gaze upon my problem. I do not
want to muddy the waters with my garbled thoughts, so please ask yourself the


Keeping in mind that "Success is the only option," If faced with a similar
task what would you do to locate the unaddressed parcels? 


Thank you in advance for any ideas.


Keith Sandell

Correctional Services Assistant Consultant

Bureau of Probation and Parole Field Services

Office of Community Corrections

Florida Department of Corrections

2601 Blairstione Road

Tallahassee, Florida 32399

Phone: (850) 410-3045 SC 210-3045

Fax: (850) 487-4427 SC 277-4427




This electronic message may contain protected health record/care information
intended for addressee(s) only. Unauthorized release or disclosure may
violate state and/or federal laws.

The Department of Environmental 

Protection values your feedback as a customer. DEP Secretary Michael W. Sole is committed to continuously assessing and 

improving the level and quality of services provided to you. Please take a few minutes to comment on the quality of 

service you received. Copy the url below to a web browser to complete the DEP 

survey: Thank you in advance for completing the survey.
-------------- next part --------------
An HTML attachment was scrubbed...

More information about the SHRUG-L mailing list