New answers tagged network
Removed the previous links, which I should have checked more scrutinously, and found some information and shapefiles which hopefully would be of some use: The EEZ Boundaries (Exclusive Economic Zone) which for this purpose is mainly used to show the coastal lines and outlines of continents. http://www.marineregions.org/downloads.php#eez The main Global ...
As for the second part of your question, v.build.polylines will connect line "segments", removing nodes as long as exactly two line segments are connected. All intersections with 3 or more segments will be left as nodes. I Can't help with the list of nearest neighbors.
i) seems like nearest point analysis; it is available in ArcGIS, and in GME (search Hawths Tools (Spatial Ecology)), ii) a line clean should sort this out
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