Matthew H. Riggs and Robert J. Krumm
PROCEDURES FOR IMPLEMENTING A SENSITIVE GIS PROJECT
ABSTRACT
The Illinois State Geological Survey (ISGS) is currently involved in a
project to help find a site for a Low Level Radioactive Waste (LLRW)
disposal facility in Illinois. The ISGS role is a two step process. An initial
statewide screening, at 1:500,000 using available data, will be used to help
identify ten or more areas which appear to meet specified criteria. These
areas will then be subjected to a more detailed, (larger scale) geological
analysis. The geology and hydrogeology of the areas will be summarized in
a written report. To date, most of our work has focused on preparing GIS
databases for the screening process. This project has required us to develop
technical procedures for several GIS-related tasks, establish techniques for
quality assurance, and compile documentation for many data sets.
Database preparation has involved extensive review of existing coverages,
including a detailed quality assurance/quality control (QA/QC) component.
Coverage tracking sheets were created to provide a written record of the
QA/QC process. New coverages have been compiled for the screening
using the same QA/QC guidelines. Metadata files are being created using
ArcInfo's DOCUMENT feature for both the existing and new coverages.
Several technical procedures have been written to cover data entry, map
digitizing, raster to vector conversion and editing, coverage documentation
and use of GPS for field verification of the locations of the wells, which are
the principle sources of geological data. These procedures were developed
to ensure that appropriate and consistent steps have been followed to
maintain high standards for compiling GIS databases.
INTRODUCTION
Amendments to the Illinois Low-Level Radioactive Waste (LLRW)
Management Act in 1987 and 1988 created the LLRW Task Group, a
committee appointed by the Governor and charged with developing criteria
to be used for siting a LLRW disposal facility in Illinois. The Illinois State
Geological Survey (ISGS) and the Illinois State Water Survey are then to
screen the State of Illinois to identify ten (or more) locations that appear
likely to meet the screening criteria adopted by the Task Group. The Illinois
Geographic Information System (IGIS) will be used to integrate both new
and existing data sets mostly at a scale of 1:500,000 for various natural
resource features and identify areas within Illinois where subsequent, more
detailed (larger scale 1:100,000) analysis of the geology and hydrogeology
will be targeted. The more detailed analysis will involve a review of all
available data, including well log and bore hole information available in the
Geologic Records Unit at the ISGS.
TECHNICAL PROCEDURES
The ISGS is preparing both GIS and tabular databases for use in the
screening by inputting geological data from well records, compiling new
coverages and editing existing coverages. In addition, we are compiling
metadata files for any coverage that may be required for screening, and
developing a QA/QC procedure for updating and compiling coverages.
Technical procedures have been written to assure that appropriate and
consistent steps are followed while compiling, editing and entering data into
the project databases. These procedures were developed to serve both as
"how to" instructions for novice data entry operators and to establish
standard methods for many of the ArcInfo processes. The procedures
address well data entry, map digitizing, raster/vector data conversion,
coverage processing and Quality Assurance Review, coverage
documentation, and the use of a global positioning system (GPS) to verify
the locations of wells in the field.
Well Data Entry
The ISGS is a repository for information about wells drilled in Illinois,
including logs of water wells, oil and gas wells, engineering borings, and a
variety of other geologic test borings. The database consists of a header file
and a units file. The header file contains information about the well, i.e.,
location, date drilled, property owner, and well type. The units file contains
a listing of the geologic descriptions (including material type and thickness)
of the materials encountered during the drilling process. The header
information is related to the units file by a unique well number.
The written technical procedure for well data entry, established as part of an
effort to enter well log information that had not been previously automated,
consists of the following three basic documents: 1) Well Database
Guidelines for Data Handling; 2) Well Data Entry System Field
Explanations and Descriptions, and 3) a listing of accepted Well Status
Codes and Abbreviations. Prior to this project, approximately 114,000
water wells with driller's descriptions had been entered into the ISGS
Oracle-based well data file. Data entry operators working on this project
have coded information from an additional 57,000 wells into the database.
These additional data will allow us to develop more accurate representations
of the subsurface geology that will aid in evaluating the ten (or more)
candidate locations.
Map Digitizing
Digitizing techniques, both manual and scanning (raster-to-vector
conversion with ArcScan), are used by the project staff to create new
coverages and update or revise existing coverages. Many variables must be
addressed to accurately transfer map products into digital format, mainly
due to the variety of source maps used. Several characteristics of the hard
copy map can determine the accuracy and quality of the digital product.
These include (but are not limited to) the original map scale, the medium on
which the map is printed (paper, mylar, vellum, etc.), the physical condition
of the map, and the amount of care taken in originally placing features on
the map.
The written technical procedure for map digitizing outlines the steps
required to create accurate and consistent coverages and lists acceptable
values for tolerance settings (i.e., weed, nodesnap, and arcsnap values) and
root mean square (RMS) error, the error values that represent the difference
between original and new coordinate locations calculated by the
transformation process. Additional procedures address checking the
digitizing board to assure it is operating properly, following detailed
instructions to promote consistent digitizing, trying to obtain maps on a
stable base (mylar), locating original work maps (which are often drawn at a
larger scale than the final published version), and checking digital products
carefully to ensure the work conforms to line-width accuracy.
Raster-to-Vector Data Conversion
Applying raster-to-vector conversion routines (ArcScan) to image files
created by scanning maps is another method for automating coverages
employed for this project. Our written technical procedures outline the steps
to be followed when: automating the map; rectifying the image to real-world
coordinates; importing the rectified image so it can be used with the GRID
command; processing and "cleaning up" the grid using ArcScan, and
converting the grid to vector coverages.
Coverage Processing and Quality Assurance Review
These written procedures include the methods used for processing and
editing coverages, checking the accuracy of digital map features and
attributes, and project QA/QC review (a multi-step operation). The written
procedures for basic coverage processing include locating and correcting
dangling arcs, building coverage topology, and assigning map attributes.
To aid the later QA/QC review, the operator in charge of the coverage
completes a tracking sheet that provides a written record for the project
archive of all information pertaining to the coverage automation procedure.
This includes the source map (or maps) used for digitizing; identification
and location of TICS used for registering; RMS values incurred during
digitizing; tolerances used for building and cleaning the coverage, and
topology processing information.
For the QA/QC review of the coverage, at least two members of the project
staff independently use a light table to check plotted versions of the line
work against the original source map to ensure line width accuracy of the
data. Color-shaded plots are then used to verify polygon and line attribute
data. The QA/QC tracking sheets includes space for recording the names of
the reviewers, dates when reviews were performed, what features were
reviewed, whether any additional editing is required, and any supplimental
information that may have been noted during the review.
Coverage Documentation
Critical to any GIS dataset is documentation (or metadata) of how the
information was compiled. This record is of particular concern when the
data are to be used for a potentially controversial or highly visible project
such as siting the LLRW disposal facility. The written procedure outlines
the techniques used to generate metadata for the digital map files used in the
screening process. The ArcInfo DOCUMENT feature is currently being
used to create the on-line metadata, but other metadata generation tools are
being evaluated. The on-line file contains a description of the dataset's
contents, statements on the data's accuracy, the history of the data, a
description of all attribute items (and their values), who to contact for
information, and other useful data. The goal is to create a document file
which conforms to Federal Geographic Data Committee standards. The
project staff has also compiled an extensive file of basic documentation
(i.e., data set names, brief descriptions, contact information, directory
location) for over 300 coverages. This information is maintained on-line as
an ASCII file and a short PERL script is used to perform key-word searches
of the file.
GPS Well Verification
During the detailed study of the ten or more candidate areas, locations of
selected boreholes in the areas will be verified in the field using a global
positioning system. Accurate locations and elevations for boreholes are
essential for constructing accurate 3-dimensional representations of the
subsurface geology of the areas. The written technical procedure for
verifying well locations documents the methods to be used in the field as
well as for processing of the GPS data. Several field teams will be working
to verify well locations and these written instructions will help ensure
consistency among the teams.
CONCLUSIONS
The Illinois LLRW disposal facility statewide screening project demands
especially careful attention to detail when compiling or using GIS datasets.
The results of this project will be distributed statewide and our methods may
be subjected to a high level of critical review. A series of written technical
procedures (along with a quality control review process) have been
developed to address this concern and they are instrumental in documenting
coverage processing and ensuring consistent handling of the GIS datasets
by all members of the project staff. QA/QC analysis and reviews of existing
and new coverages has greatly improved the overall quality of our in-house
data holdings.
The ISGS continues to refine its technical procedures for compiling and
digitizing new data, evaluating existing digital data, and adding on-line
metadata files to the IGIS. All technical procedures and additional materials
are available via the ISGS home page at the following URL:
http://www.isgs.uiuc.edu/isgshome.html.
Acknowledgments:
Contributions to this paper have been made by a number of our colleagues,
including Curtis Abert, Sally Denhart, Sandrine Elinski, Paul Jahn, Alison
Lecouris, Daniel Nelson, Richard Rice and C. Pius Weibel. The concepts,
ideas, and accomplishments described in this paper would not have been
possible without their contributions and continued support and involvement.
Matthew H. Riggs, Associate Geologist
Robert J. Krumm, Geologist and Section Head
Geospatial Analysis and Modeling
Illinois State Geological Survey
615 E. Peabody Drive
Champaign, Illinois 61820
Telephone: (217) 244-2425; (217)333-4085
Fax (217) 333-2830
E-mail: riggs@tully.isgs.uiuc.edu; krumm@zydeco.isgs.uiuc.edu