Thoughts about performance improvements

[xeophin]

… based on partially running the process locally:

The thing that really, really takes a long time is clipping the borders to the land masses. As far as I understood it this happens for every country separately, and with the non-simplified version of the data.

1. Combine all countries and subdivisions in one Topojson file -> drastically smaller file size compared to GeoJSON, data format is «closer» to how Mapshaper works
2. Simplify the combined Topojson file with Mapshaper -> only needs to run once, and makes sure that all borders will fit each other, since the data is topological
3. Simplify the landmass data with Mapshaper -> we don't need every single little island off the coast
4. Now do the clipping on the whole Topojson -> only needs to run once, and the reduced number of points should make the process faster
5. Split the Topojson apart as needed (or use the Topojson directly to generate the vector tiles, if supported?)