The coverage extent represents the outer boundary of a coverage. It is the minimum bounding rectangle that defines the coordinate limits (extreme minimum and maximum coordinates) of coverage arcs; label points; and by definition, polygons, route systems, and regions.
The geographic extent information for a coverage is stored in the bnd.adf file. The bnd.adf file is used by many Esri software applications to set the geographic extent for drawing a coverage. In addition, it is often used as a default map extent for quick coverage display. Many spatial processes use the bnd.adf file to determine whether one coverage overlaps another and to sort coverage features by location for processing.
The BND file contains the following items:
The x-coordinate of the coverage extent's lower left corner
The y-coordinate of the coverage extent's lower left corner
The x-coordinate of the coverage extent's upper right corner
The y-coordinate of the coverage extent's upper right corner
The coordinates for links, tics, and annotation can fall outside the bnd.adf file. A coverage containing no arcs or label points (or a single label point) will have an undefined bnd.adf.
Usually ArcGIS maintains the extent for you, updating it as you add features to, or remove features from, a coverage. If for some reason the extent shown does not match the actual extent of the features, click Fit on the Coverage Properties dialog box to recalculate the coverage's extent. Alternatively, you can type new extent values into the appropriate text boxes.