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This clipping point potentially exists in several Tile-LODs having a common boundary; in which case, all points representing the same clipping point share the same JID. Doing so ensures that
connectivity between geocells and tiles is preserved. A clipping point can be identified by the application by checking the 2D relationship tile connection file. There is a 2D relationship tile
connection file per network dataset tile. When the file is missing, it indicates there is no clipping point for the lineals belonging to the tile. The 2D relationship file is a dBASE file that contains a
list of records made of 2 attributes; the Junction ID JID that identifies the start or end point of the clipped linear and the Network Component Selector 1 NCS1 that identifies the network
dataset lineal file. The dataset code file is implicit to the network dataset tile directory and the Network Component Selector 2 always represents a linear feature vector features code 003 thus
do not require to be included in the record. The coordinate of the tile adjacent to a clipping point can be determined using the latitude and longitude of that point.
If a connection between two linear features happens to be located exactly at a tile boundary, the lineal is obviously not clipped but a junction ID is allocated and included in the 2D relationship
tile connection file.
In a 2D relationship tile connection file, no two records are identical; however JIDs may appear more than once with different NCS1, indicating a connection between network subdatasets.
5.7.1.6.2 2D Relationship Dataset Connection File
The CDB Topological network is made of several network datasets that in turn are made of several vector files such as ShapeFiles. By specifying a junction identifier per feature, any
features in any of these several vector files can in theory be connected to any other features located in a separate files such as Shapefiles. A connection within a tile, which includes the
tile boundaries, can be identified by the application by checking the 2D relationship dataset connection file. There is a 2D relationship dataset connection file per network dataset tile. This
file contains all the connections between the sub-datasets of the corresponding network dataset with other network datasets. When the file is missing, it indicates there are no connections
within the tile. The 2D relationship file is a database or other file that contains a list of records made of 4 attributes; the Junction ID JID that identifies the connected point, lineal or polygon
features, the Network Dataset Code NDSC that identifies the network dataset the feature belongs to, and the Network Component Selectors NCS1 and NCS2 that identify the network
sub-dataset and the shape type. The tile coordinate and tile LOD is implicit to the Network Dataset tile directory.
All the records in the 2D relationship file are sorted per ascending JID. This has two advantages; it speeds up the search process when looking for a specific JID and it groups all the features that
are connected together. In effect, there is always a minimum of two consecutive records with the same JID; the record belonging to the corresponding file dataset or sub-dataset and the record
identifying the feature it connects to. Note that when a 2D relationship file specifies a connection to a feature belonging to different network dataset, the corresponding LOD file of
this dataset may or may not exist. If the corresponding LOD file of the target dataset is missing, the application must look for the feature in the coarser LOD file of the target dataset. If the
corresponding LOD file of the target dataset exists, the feature may be missing because it has
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been removed by the off-line tool decimation process; when this is the case, the application must look for the feature in the finer LOD file of the target dataset.
5.7.1.6.3 Junction Identifier SJID, EJID, and JID Range
