Creation of administrative level classified polylines from COD-AB polygons

One of the desirable features for COD-AB datasets is a line shapefile with codes 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 so that, for instance, they avoid an administrative level 2 boundary symbol appearing along an international border.  ITOS makes these line shapefiles when they process your countries but if you are not yet ITOS processed you can also make them yourself with these instructions 

The process may be unnecessary for island, landlocked, or enclave countries containing only administrative level 0 polygons because all boundary lines will have the same status but it may still be useful for consistency and differentiating international borders from coastlines.  The process is advised for all other countries for proper cartography.

Step-by-step guide

• Create the polyline shapefile, either with ArcGIS Advanced or ET GeoTools.    FIS will soon test QGIS for this process.
  • ArcGIS Advanced option (option 1 of 2):

    • Run the ArcGIS ‘Polygon to Polyline’ tool (Toolbox > Data Management Tools > Features > Polygon To Line) with:  "Input Features" = (input polygon shapefile); "Output Feature Class" = (as desired); "Identify and store polygon neighboring information (optional)" selected; and all environment settings set as default.

Example Polygon To Line output

• ET GeoWizard option (two steps) (option 2 of 2):
• Step 1:  Run the ‘Polygon to Polyline’ tool

This will create lines that close all polygons - one line per polygon.

Step 2:  Run the ‘Clean PolyLine Layer’ tool

The remaining processes are completed in ArcGIS, regardless of whether ArcGIS or ET GeoWizards was used for the creation of the line shapefile.

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

• 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)
• (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
• 
• Click ‘OK’
• Set a definition query to exclude the ‘NULL’ values of the input polygon shapefile.  (This might refer to a .FID or a .OBJECTID)

• This should reveal the internal boundary lines.  (External boundary lines are deselected because they border the outside of the country and received a 'NULL' left polygon identifyier.  THIS WORDING CAN BE IMPROVED.)
• 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.

• Administrative levels in boundary polygon shapefile	Required calculations
  Administrative level 0
  Administrative levels 0 and 1	polyline shapefile RIGHT_A0 = polygon shapefile Adm0code
  Administrative levels 0, 1, and 2	polyline shapefile RIGHT_A0 = polygon shapefile Adm0code polyline shapefile RIGHT_A1 = polygon shapefile Adm1code
  Administrative levels 0, 1, 2, and 3	polyline shapefile RIGHT_A0 = polygon shapefile Adm0code polyline shapefile RIGHT_A1 = polygon shapefile Adm1code polyline shapefile RIGHT_A2 = polygon shapefile Adm2code

[IF THIS DOES NOT WORK, ENTER ' "LEFT_A0" IS NULL']

• Open attribute table and calculate AdminLevel = 0
• (Unless the Adm0 lines are all shoreline or all international boundary ... IN WHICH CASE....) 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

• Set a definition query for LEFT_A0 = RIGHT_A0 and LEFT_A1 <> RIGHT_A1; calculate AdminLevel  = 1.

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

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

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