Add ocean basins and subbasins

[jbusecke]

• Closes Exploring the addition of 'Ocean Basin' regions #697

This is my first attempt to add larger scale ocean basins (derived from the marine_regions polygons). I basically just followed @nvkelso s instructions in #697 and that seems to work reasonably well.

I have so far only looked at the large scale ocean basins, and noticed one oddity:
In Addition to the regions I expected, there is a small strip (I belive along the West Coast of Africa) that has the name "None". I plotted the shape in geopandas

import geopandas as gpd
basins = gpd.read_file('10m_physical/ne_10m_oceanbasin.shp')
basins.iloc[[11]].plot(figsize=[20,14])

Any suggestions how to deal with this region? Does that need to be addressed in the 'marine_poly' source?

Once that is resolved, would the addition of the shapefiles be enough, or should I document exactly the steps I have taken to arrive there?

For posteriority this is what I did on my local machine:

1. Install Node.js (was already installed)
2. npm install -g mapshaper
3. git clone my_fork_of_natural_earth
4. mapshaper -i 10m_physical/ne_10m_geography_marine_polys.shp -dissolve oceanbasin -o 10m_physical/ne_10m_oceanbasin.shp
5. mapshaper -i 10m_physical/ne_10m_geography_marine_polys.shp -dissolve subbasin copy-fields=oceanbasin -o 10m_physical/ne_10m_subbasin.s