GCDB AND USGS PLSS

(Now known as CADASTRAL REFERENCE WORKGROUP)

ISSUES AND OPPORTUNITIES

April 18, 2008

9:00 – 11:30 a.m.

Revised Minutes

 

Attendees:

Name

Organization

Email

Phone

Gail Ewart

IGO/OCIO/DOA

gail.ewart@cio.idaho.gov

332-1879

Jeff Servatius

ISTC

jservatius@tax.idaho.gov

334-7750

Anne Kawalec

Ada County Assessor's Office

akawalec@adaweb.net

287-7261

Walt Bulawa

ISTC

wbulawa@tax.idaho.gov

334-7718

Bob Smith

IGO/OCIO

robert.smith@cio.idaho.gov

332-1867

Gary Wilbert

Idaho Power

gwilbert@idahopower.com

388-2429

Michael Ciscell

IDWR

michael.ciscell@idwr.idaho.gov

287-4915

Kevin DeRossett

BLM

kevin.derossett@blm.gov

373-3990

Jack Clark

Ada County Assessor's Office

asclarjm@adaweb.net

287-7266

 

Brief introductions were made.

 

Gail Ewart has asked Sheldon Bluestein to be the lead for this committee.  Anne Kawalec will be assisting Sheldon in that effort.

 

Glossary:

  We began a discussion on glossary terms that differ in the survey world and the GIS world.  The following words will be added to a glossary that will be posted on the website.

 

  1. Control – Because GIS is not meant as a replacement for surveying, we need to be more careful in our terminology when speaking about control. 

 

 a. Survey Control – Marc Thomas has provided the following definition for “control” as used in the GCDB: Control is the term we use to describe a PLSS corner that has coordinate values attached to it by some physical means, i.e., aero triangulation via aerial photography, conventional survey ties to horizontal control (triangulation stations), GPS observations, or digitized from USGS 7-½ minute topographic quadrangle maps (recovered PLSS corners indicated with a bold tick).

           

b. GIS Control/Cadastral Reference – Donna suggested that frequently, when GIS professionals use the term “control” what we are really talking about is Cadastral Reference.  The Cadastral NSDI Reference Document defines Cadastral Reference as the set of information that allows parcel level information to be registered to other data themes and to be tied to features on the ground. Cadastral reference is composed of the spatial reference data (geodetic control and orthophotography) and survey frameworks such as the Public Land Survey System (PLSS), parcel map grids, subdivision boundaries or municipal boundaries. Parcels are nested into and tied to the reference data and the cadastral reference.

 

Control vs. Cadastral Reference – It was suggested, by Donna, that we use ‘control’ to discuss point control but use ‘cadastral reference’ to discuss the fishnet of lines and points that used to tie GIS data to the PLSS.

 

3.  GCDB - The Geographic Coordinate Database (GCDB) is a program in the Bureau of Land Management (BLM) that supports the management of public lands, principally in the western states by managing coordinate values on Public Land Survey System (PLSS) corners and special survey areas.

 

4.  GCDB PLSS – GCDB-derived PLSS digital map layer used for parcel mapping.

 

5.  24K PLSS – The rectangular, section level grid shown on USGS 1:24K quadrangle maps and digitally available through Digital Line Graphs (DLG) and SDTS (Spatial Data Transfer Standard)

 

6.  Accuracy - the degree of conformity of a measured or calculated quantity to its actual (true) value

 

7.  Precision - characterises the degree of mutual agreement among a series of individual measurements, values, or results; repeatability

 

8.  Reliability of coordinates - used to express the expected positional accuracy, relative to the earth's surface.

 

 

County Inventory, Idaho State Tax and RAVAR:

Marc Thomas discussed the FGDC parcel inventory and asked what PLSS (TRS) each county is using.  There are at least three different organizations doing surveys for parcel data.   Dixie Booker-Lair, IDL, has sent out a survey to gather info from counties about their mapping data.  With so many different surveys, we discussed the need to consolidate our efforts.  It was suggested that we talk with Chris James, Assessor’s mapping Committee Chairperson.  Jeff has done a survey in the past and has offered to ‘blend’ the results and deliver it to Chris.

 

Resources Available – Data Standards:

Bob Smith, Office of the IGO (Idaho Geospatial Office), and Walt Bulawa, ISTC (Idaho State Tax Commission), have been looking for a PLSS layer to use with the ISTC statewide parcel data.  Walt has sent the following summary of their project:

 

We have downloaded over 1400 SDTS files from the USGS, decoded them and merged them into a single feature class in an effort to produce a Cadastral Digital Reference feature that would present the PLSS for the entire state of Idaho at an acceptable accuracy when viewed at a scale of 24K.  We added DLG-derived data to fill in some of the voids in the USGS SDTS data.  We then carefully digitized the section lines from digital raster DRG maps to fill some of the remaining voids.  After the feature was created, we then quality control checked each of the greater than 79,000 sections at a scale of between 10K and 24K to ensure that the product that we produced adequately presented the 24K PLSS as shown on the 24K DRGs.  Also, for correction, we did not at any time use the roads layer from Inside Idaho.

 

More Long-term solutions:

  • We discussed the benefits of having a State Surveyor to help lead an effort to provide all the ID counties with better survey control. 
  • A State Surveyor would provide the state with a subject matter expert and a data steward for surveying data.

 

Action Items:

  • Jeff will take the lead in contacting both Marc and Dixie to consolidate the county parcel data survey questions.  They will then provide the survey to Chris James who will then share it with the assessor’s community.

 

  • Sheldon will put together a presentation on the past, present and future of the GCDB.

 

Next Meeting:

May 23rd, 9:00 a.m.

IDWR has kindly offered to host our next meeting so that we can use their GoToMeeting technology.

Details to follow.