ERROR
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.
Note:
The working units are those you'll specify the travel time or distance under the costs column in the problem definition dialog.
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