How Append (Coverage) works

Append combines features from two or more coverages into a single output coverage. It does not calculate new topological relationships between the resulting features. This is accomplished by running Build or Clean after the coverages have been combined. The FEATURES_ONLY option can be used to merge different feature types (for example, points from one coverage and arcs from another). With FEATURES_ONLY, only coordinates are appended; feature attribute tables are neither appended nor copied.

ID offsets can be used to modify User-IDs for tics, features, or both in the Output Coverage. Before a coverage is appended, the offset is calculated as one plus the largest User-ID value for the specified feature class that has been written to the Output Coverage so far. The offset is then added to each feature User-ID in the appended coverage; thus, Output Coverage User-ID = input coverage User-ID + offset. Offsets are not applied to the first coverage. (See the table below for an example of offset calculations for tics.)

If the NO option is specified as the offset type, no User-ID will be modified. If the appended coverages contain duplicate Tic-IDs, any previously encountered Tic-ID will not be written to the Output Coverage. This is useful when each tic in the study area has been digitized with one unique Tic-ID. If the feature attribute tables of the appended coverages contain duplicate User-IDs, the Output Coverage will contain duplicate User-IDs for arcs or label points.

Coverages created with APPEND generally require further processing before other coverage tools can be used on them. This may include

• Splitting intersecting arcs (for example, by Clean).
• Removing sliver polygons or boundaries between adjacent coverages (for example, by Eliminate, Select, or Dissolve).
• Removing dangling arcs (for example, by Clean).
• Dissolving interior boundaries between adjacent coverages (for example, by Dissolve).
• Building topology (for example, by Clean or Build).

Adjacent input coverages should meet accurately at their shared boundaries. If two coverages share a common boundary, the arc coordinates that define the common boundary should ideally be the same for both coverages. Equally important, arcs that meet at borders between adjacent coverages should match. Polygon codes should be the same if a polygon extends across a border and into an adjacent coverage.

Coverages can also be vertically appended. If the Input Coverages contain different feature classes, the FEATURES_ONLY option can be used. If you want to merge feature attributes into the Output Coverage after Append with FEATURES_ONLY, do not use a feature User-ID offset. After Append, you can use Join Info Tables to merge pre-existing attributes from the old coverage feature attribute table into the Append Output Coverage.