When the Feature Class to Coverage tool is used to convert polygon or line feature classes or shapefiles to an ArcInfo coverage, the attributes are lost.
Polygon feature classes and shapefiles can include discontiguous (multipart) polygons, polygons with 'donut holes', and overlapping polygons.
In the ArcInfo coverage data model, polygons cannot be discontiguous, cannot have 'donut holes', and cannot overlap. In a coverage, these features are maintained in a REGION subclass. To keep the attributes, polygons from a feature class or shapefile must be converted to a REGION subclass in the coverage.
Line feature classes and shapefiles can have thousands of vertices that define the position of a single line feature.
In the ArcInfo coverage data model, line features are limited to 499 vertices. In a line coverage, ArcInfo automatically creates a node at the 500th vertex and begins a new arc. To maintain attributes along the entire length of the input line feature in the output coverage, the line feature must be converted to a ROUTE subclass.
Solution or Workaround
To maintain data accuracy and attributes for polygon or line features when converting to a coverage, follow the steps below.
- In ArcToolbox, right-click ArcToolbox at the top of the Favorites tab, and select Environments.
- Open Coverage Settings, and set both Precision for Derived Coverages and Precision for New Coverages to DOUBLE. Click OK.
- Right-click ArcToolbox again and select Save Settings > To Default. The precision and accuracy of the input data is maintained in the output coverage.
- When a polygon feature class or shapefile is converted to a coverage, the output TYPE must be REGION.
If the input polygon data includes discontiguous polygons, overlapping polygons, or 'donut holes', the coverage must be maintained as a REGION coverage, with the attributes stored in the region subclass.
After creating the output REGION coverage, the attributes can be transferred from the REGION subclass to the coverage polygons. Refer to step 6 in the article 'Convert a polygon shapefile to a coverage using SHAPEARC' under the Related Information below for instructions.
The REGIONPOLY command requires an <out_table> to retain the attributes. If an <out_table> name is not specified in the command line, the attributes will be lost.
- When a line feature class or shapefile is being converted to a coverage, the output TYPE must be ROUTE.
To transfer ROUTE attributes to ARC features in the coverage, run the following commands at the ArcInfo Workstation command line:
PRECISION double double
ROUTEARC <in_cover> <route_system> <out_cover>
A new coverage, created with the Feature Class to Coverage tool or by REGIONPOLY and ROUTEARC, does not have its projection defined. Use the PROJECTDEFINE command at the ArcInfo command line to define the projection for the coverage with the same parameters as the projection definition from the input feature class or shapefile.
- The FUZZY tolerance setting for the new coverage is critically important when processing the coverage.
A. To set the FUZZY tolerance setting, go to ArcToolbox > Coverage Tools > Data Management > Tolerances tool.
B. In the Tolerances tool, select the new coverage as the input and accept the default Tolerance Type, FUZZY.
C. Type in the Tolerance Value.
• If the coverage is in a geographic coordinate system, with units of decimal degrees, type in the following Tolerance Value:
• If the coverage is in a projected coordinate system, with units of feet or meters, type in the following Tolerance Value:
These very small values preserve the precision and accuracy of coverage features in future processing.