One of the desirable features for COD-AB datasets is a line shapefile with an 'admlevel' attribute field designating the administrative level of each line segment i.e., '0' representing international borders (but '99' representing coastlines), '1' representing lines between distinct administrative level 1 units, etc.  These files are necessary for the best cartographic symbology.  The alternative is to symbolize all polygon boundaries so that higher level boundaries have multiple symbols.  (Even if these are carefully disguised by symbol size and order, shorelines cannot be symbolized properly.)  ITOS makes these line shapefiles when they process your countries but if a country is  not yet ITOS processed the coded line file can also be made with these instructions.

The process may be unnecessary for island or landlocked countries containing only administrative level 0 polygons.

INSERT EXAMPLE 

STEP 1:  Create the polyline shapefile. 

The goal is to create a shapefile with individual line features between nodes and left and right polygon identifiers.  (Polygon shapefile exterior features have their left polygon identified as '-1'.)  This process is discussed below for four software environments.

The remaining processes are completed in ArcGIS, regardless of the software environment used above.

STEP 2:  PREPARE THE P-CODE FIELDS IN THE POLYLINE SHAPEFILE

• Add fields to the output boundary polyline shapefile as follows:

Note that in the unusual case of numeric P-codes, the new fields should be of the same type.

• Verify that the AdmLevel values have all been set to zero.  Calculate them to zero if they are not.

STEP 3:  POPULATE THE POLYLINE P-CODE FIELDS

• Right-click the polyline shapefile > "Joins & Relates" > "Join..." (or properties > Joins & Relates) and provide the Join Data as follows:
• "What do you want to join to this layer?" = Join attributes from a table
• "Choose the field in this layer that the join will be based on:" = LEFT_FID
• "Choose the table to join to this layer, or load the table from disk:"  = (the input polygon shapefile)
• "Choose the field in the table to base the join on:" = OBJECTID (or FID)
• Select "Keep only matching records".  These will be the line features that are not boarding the sea or a neighboring country.

• Optionally, click the ‘Validate Join’ button.  Do not expect all records to match - because the ‘left’ side of all exterior lines will have no neighboring polygon.  Do not worry if you receive a “Field names that match reserved words should not be used in database schema and can cause the join to fail. The following fields match reserved words….” message.  Close the 'Join Validation' dialogue box after inspecting the result.

• Click ‘OK’
• Begin editing the polyline shapefile
• Open the output polyline shapefile attribute table
• Use the Field Calculator to calculate all the LEFT_Ax values (for the LEFT_Ax fileds recently added to the polyline shapefile ) equal to the coresponding administrative levels of the polygon shapefile.

• Close the attribute table, remove the join, and establish a new join basing on RIGHT_FID.  Anticipate all records matching.
• This time there should be no need to make a definition query, as there should be no null values.
• Open the output polyline shapefile attribute table.
• Use the Field Calculator to calculate all the RIGHT_Ax values (for the RIGHT_Ax fileds recently added to the polyline shapefile ) equal to the coresponding administrative levels of the polygon shapefile.
• Create a definition query to select the line segments with different LEFT_A0 and RIGHT_A0 attributes.

• Remove all joins

STEP 4:  CALCULATE THE ADMINISTRATION LEVELS

ADMINISTRATIVE LEVEL 0

• Open attribute table and calculate AdminLevel = 0 for all features.  (Higher administrative level features will be adjusted later.) 

Recall that shoreline features need to be coded specially as '99'.  If the country has a shoreline follow the SHORELINE TREATMENT steps.

SHORELINE TREATMENT

• Open an editing session for the line shapefile.
• Manually select line segments that represent shorelines (splitting line segments where an international border meets the water).  It may be useful to add a world country layer or neighboring country layers.

• calculate AdminLevel  = 99.

Check carefully for discontinuities

HIGHER ADMINISTRATIVE LEVELS

Administrative level 1

Set a definition query for LEFT_A0 = RIGHT_A0 and LEFT_A1 <> RIGHT_A1.  

Set a definition query for LEFT_A1 = RIGHT_A1 and LEFT_A2 <> RIGHT_A2; calculate AdminLevel = 2.

ISet a definition query for LEFT_A2 = RIGHT_A2; calculate AdminLevel  = 3.

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