Merging and Joining Land Cover and Land Use Areas

Often times, Land Use (LU) and Land Cover (LC) Area features are represented by multiple polygons. This can result in LU and LC official names being displayed multiple times in an application. Merging and Joining of these polygons resolves this problem. The following rules are followed in order to merge or join LU and LC areas correctly:

Joining an LU or LC Area that is entirely in an Order 8 Area

Join all parts of an LC or LU, that are the same LC or LU feature, and that have the same attributes and the same Official Name.
If an Official Name is not present for a polygon, no joining is allowed.

Merging an LU or LC Area that crosses an Order 8 Area to an Adjacent Order 8 Area

Merge only parts of LC or LU areas, when:
- they are adjacent at the Order 8 border; AND
- the same Official Name for the same language code is available; AND
- all other attributes are equal.
Never merge part of Land Cover or Land Use when adjacent at the Order 8 border if the same Official Name for the same language code is not available.
Parts of the same object have to be adjacent at the Order 8 border in order to be subject to merging even if they have the same Official Name:

An Exception to the Merging Rules

Display Features that are face based and adjacent have to be merged within the Order 8 Area. The adjacent faces are merged to one object for one feature type, even if they have no Official Name. Non-adjacent faces result in separate polygons.

Results of Merging and Joining of LU and LC Areas in GDF

GDF Section Crossing Features with Adjacent Parts at Section Border that have an Official Name

Joining and merging, applied before sectioning, has the following result:

The object receives the highest identifier of the composing original parts.
Sectioning on product has the following results:
The identifier is equal in each section where the object resides.
The split indicator is set to 1 for each object part in the sections.
Conversion records are generated from each object part to the parts in the adjacent sections.

GDF Features in Adjacent Sections but No Adjacent Parts but have the same Official Name

Joining and merging, applied before sectioning, has the following result:

• The non-adjacent parts remain separate objects and have different identifiers.
Sectioning on product has the following results:
The non-adjacent parts remain separate objects with different identifiers.
The split indicator is set to 0 for each object in each section.
No Conversion records are generated.
See figure below.

Figure: GDF Features in Adjacent Sections but No Adjacent Parts

Features with No Official Name in a Section

Joining and merging is not performed for these features unless they are face-based and adjacent.