2.0 KiB
README World Map GeoPackage
The world_map.gpkg contains the following layers:
- countries
- states_provinces
- disputed_borders
These layers were processed from source data. The purpose of this readme is to explain briefly the data sources and the processing steps.
Data source
Natural Earth 1:10m detail level Cultural vectors: https://www.naturalearthdata.com/downloads/10m-cultural-vectors/
The specific layers used for input are:
[0]: Admin 1 – States, Provinces v4.1.0
[1]: Admin 0 – Countries v4.1.0
[2]: Admin 0 – Breakaway, Disputed Areas v4.1.0 (boundary lines)
Processing
The layer-specific processing steps are described below.
countries and states_provinces
These two layers are derived from data source [0].
In order to keep the size small, the geometry was simplified with GRASS v.generalize, then dissolved
on state/province level and on country level respectively. These above steps were done with a QGIS model world_map_generalize.model3 that is included in this folder.
For the countries layer, the attribute table of data source [1] was joined in manually and the country attribute fields were copied.
Side notes to the QGIS model:
-
Input data are in WGS84 (EPSG:4326); re-projection to a meter-based CRS was necessary in order to set meaningful thresholds in
v.generalize. I chose Robinson (EPSG:54030) for that purpose. I think it is an OK compromise for a global projected CRS in this case. -
The model also creates a safe extent polygon for WGS84 coordinate space and clips the simplified layers to that extent before re-projecting them back to WGS84. This was necessary in order to avoid polygons crossing the 180˚ meridian. Those would be rendered as large invalid polygons crossing the entire world.
disputed_borders
This layer was created by importing data source [2] as-is.
Manual clean-up of attribute tables (all layers)
Finally, in the GeoPackage the less meaningful fields in the attribute tables were dropped.