Version 4.0: Use Recommendations
The
use of geographic information systems (GIS) in managing and analyzing
environmental data in Oregon is becoming widespread. Although
GIS technology has been available for 25 years or so, recent technological
advancements have made GIS available to many desktop computers users.
Consequently, the availability of spatial data sets is also increasing.
These data sets are often composed of information collected for different
reasons by different groups at different times. Consumers of
these GIS data layers include Oregon watershed groups, for example,
the Tillamook Bay National Estuary Project (TBNEP), The Coos Bay Dynamic
Estuary Management System Project (DEMIS) and now the MidCoast Watershed
Council (MCWC), all of which have made GIS central to their watershed
management projects.
Several
watershed groups in Oregon have invested heavily in GIS by acquiring
necessary computer hardware and software, training, and spatial
data sets. The strategy to develop watershed management and
monitoring plans seems to be to acquire readily available data sets
and to use GIS as a tool to store, analyze, and communicate this
information. However, like any other tool, GIS users must
be aware of important limitations, especially limitations involving
spatial data sets. Not all data are good data, and not all
good data can be used all of the time: periodically, data must be
critically reviewed for completeness and utility.
Purpose & Scope
This
project was initiated to review the GIS layers present on the MCWC
CD-ROM Ver 4.0. The CD-ROM contains all available spatial data
and readily available metadata and represents a good first effort
at an initial data inventory. The MCWC CD-ROM contains data
sets similar to those collected by two other Oregon watershed projects,
TBNEP and DEMIS.
The
purpose of this report is to review and summarize the GIS data layers
and associated data files. Information contained in this report
and in Appendix I depicts the geographic extent of each data layer,
scale, and how the layers were generated. This report also
presents use restrictions (based on the experience gained in applying
the data set to the Rock Creek Watershed and other projects) and
provides recommendations.
Summary
- There were 164 data layers
on the MCWC CD-ROM: 42 line coverages, 22 point coverages, 63
polygon coverages, 31 GRID files and 6 shape files.
- 16.1% of the layers were
at a scale of 1:24,000 or larger (i.e., 1:12,000)
- Less than half of the
layers on the CD were associated with metadata.
- The spatial error was
not documented for most layers.
- Documentation describing
the creation of each data layer was missing for most layers.
- Most layers did not have
data collection methods documented.
- Most layers did not have
data fields names documented.
Creation
of the MCWC CD-ROM was a necessary first step in developing a GIS.
This CD-ROM represents an inventory of all readily available spatial
data sets. In order to make future spatial data sets useful
for watershed analysis, the following recommendations are offered
: 1) New data layers should be developed at a 1:24,000 scale because
the GWEB manual strongly suggests that watershed analysis should
occur at this scale; 2) Methods for data layer production, including
digitization steps and accuracy assessments, need to be documented
and made available with the layer; 3) If data are to be transferred
to another base map, go back to original data; 4) Use well-documented
base maps to depict information. For example, use standard
DLG files (available from USGS) that have known spatial accuracy
and adhere to National Map Accuracy Standards. Avoid creating layers
from variable scale data; 5) For all summaries and layers created
by analysis, document both the source layers and the steps (methods)
taken to summarize layers. Make this information available with
the data layer; 6) For GIS layers that make use of data resulting
from technical studies, document the study date, researcher, methods
(protocol), how measurements were made, units of measurement, etc.;
7) Bundle all metadata with GIS layers.
Related Publications
Brophy, L. and R. J. Garono.
2000. GIS as a Tool for Watershed Assessment: Working Toward a Desktop
Decision Support System. Proceedings of the 17th International Conference
of The Coastal Society, Portland, OR USA. 592.
Garono, R. J. and L. Brophy.
1999. Using A Geographic Information System (GIS) To Prioritize
Monitoring And Restoration Activities In An Oregon Coastal Watershed.
Proceedings of American Water Research Association.
For more information
contact the
