Happened to be making some maps today, and realized 1:110m would be better than 1:10m for small world maps in R (much faster too). I had the whole Natural Earth dataset downloaded in sqlite format. SQLite is great but I can’t run spatial queries on that in Spatialite format (they store the geometries differently).

GDAL/OGR to the rescue:

ogr2ogr -f SQLite natearth_vector_spatialite.sqlite natural_earth_vector.sqlite -skip-failures -nlt PROMOTE_TO_MULTI -dsco SPATIALITE=YES

Turns out Spatialite, and I suspect Postgis, don’t like when you mix Multi and non Multi geometries if a column is declared Multi. Thankfully EvenR solved this in gdal 1.10 with -nlt PROMOTE_TO_MULTI

A few hours later, 400+MB of great base material for cartography…

Oh wait, try to dissolve countries into UN subregions, what are all those weird partial lines in the middle of what should be solid polygons? Slivers of course, places where the topology of borders are not snapped.

Solution?

  1. Processing in QGIS, GRASS tool v.dissolve, advanced set a tolerance

OR

  1. Buffer the polygons 1st before smushing (Thanks Brian)

    CREATE TABLE subregionsT AS
SELECT subregion,CastToMultiPolygon(GUnion(Buffer(Geometry,0.00001))) as geometry
FROM ne_110m_admin_0_countries
GROUP BY subregion;

Solution 1 is probably cleaner, as I don’t have to now clip the continents to match the coastline again, but solution 2 let me keep it all in the same db where the data was to start with less steps.