This error occurs while creating a service area with ArcView's Network Analyst extension, and attempting to set the cost field in the problem definition dialog box to something other than the default <Line Length>:
"Error reading impedance value"
Null data values in a numeric field of the ArcInfo coverage were used as the street theme.
Solution or Workaround
- Select, from the attribute table of the line theme, all values in the cost field that are greater than 0.
- Convert the selected records to a new shapefile.
- Click Find Service Area to display the problem definition dialog box from the Network menu.
- Click the Properties button in the problem definition dialog box.
- Specify the cost field and the working units in the Properties dialog. At this point, you will notice the error no longer appears
The working units are those you'll specify the travel time or distance under the costs column in the problem definition dialog.
- Continue with the normal process of finding a service area.