Executive Summary

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.

Project Description

  • 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.


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.