Data Sources

The primary data source for the project was the 10-meter digital elevation model (DEM) used for terrain analysis. I would have liked to have been able to use an imported vector stream channel coverage in my analysis, however the deviation from the correct location of the stream channels when importing to IDRISI was too large (see details in the errors section). Therefore, stream channels had to be derived from the DEM (a time consuming process).

Digital Elevation Model

Source: 15 7.5-minute DEM quadrangles with a 10 m grid cell resolution were downloaded from Department of Earth and Space Sciences, University of Washington. http://128.208.108.44/data/raster/tenmeter/byquad/index.html
Format: USGS ASCII DEM file.
Projection and Datum: Transverse Mercator, Zone 10 N, NAD 1927.

City Limits

Source: Downloaded from the WSDOT GeoData Distribution Catalog http://www.wsdot.wa.gov/mapsdata/geodatacatalog/default.htm
Format: ESRI Arc polygons
Projection and Datum: Transverse Mercator, Zone 10 N, NAD 1983.

Populated Places

Source: Downloaded from the WSDOT GeoData Distribution Catalog http://www.wsdot.wa.gov/mapsdata/geodatacatalog/default.htm
Format: ESRI Arc point file
Projection and Datum: Transverse Mercator, Zone 10 N, NAD 1983.

Hydrology (Stream and River channels)

Source: Downloaded from the Washington State Department of Natural Resources site at http://www3.wadnr.gov/dnrapp3/dataweb/dmmatrix.html
Format: ESRI Arc shapefile
Projection and Datum: Transverse Mercator, Zone 10 N, NAD 1983.
Note: This coverage was not used in the final analysis due to problems converting to IDRISI vector format.

Data Preparation

All of the 15 DEMs for the study area were imported into IDRISI using DEMIDRIS. They were joined together into a single coverage using CONCAT (concatenate). The excessive file size of the resulting raster image (74 MB) made many operations impossibly time-consuming. Therefore, the image was downsampled using CONTRACT, which produced an 8 MB file. This also effectively reduced the pixel resolution from 10 m to 30 m. However, since the study area was 48 km across, I felt that a 30 m resolution would be sufficient.