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COD-ABs Administrative boundaries are available for some countries are available with locations in an alternate edge-matched version (COD-EM) as well as the original definitive COD-AB version.
COD-ABs remain the definitive, accepted, best-available administrative boundary sets for each country. However, COD-EM layers may be more suitable for cartographic visualizations and might also be useful for topological analysis of lower administrative level international connectivity.
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What are COD-EMs?
COD-EMs are copies adapted versions of the original definitive COD-AB that have had their external feature polygons extended or shrunk to fit the United Nations Geo Hub 1:1m boundary. They therefore fit the COD-EM of neighbouring neighboring countries, when available. They may be suitable for cartographic visualizations and might also be useful for topological analysis of lower administrative level international connectivity.
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Where countries border each other, one or even both boundaries may be less accurate than the original, definitive boundaries. The UN Geospatial Hub boundary is generally of lower quality than the definitive COD-AB layers.
The size and shape of peripheral polygon features may have been changed. International borders are shifted to the UN boundary, either enlarging or shrinking the polygon area.
Peripheral polygon feature shapes and the relationship of their areas to those of their internal neighbouring neighboring features may be distorted, while internal features are untouched.
Peripheral polygon features may artificially appear to touch different, incorrect features belonging the same country. (An example will be illustrated if discovered.)In theory, peripheral polygon features may be eliminated. This is monitored and will be specially treated if it occurs. (An example will be illustrated if discovered.)
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