Support Choropleth's locationmode in Choroplethmapbox

[huonw]

A choropleth trace supports specifying locations as high-level string names/IDs, via the locations and locationmode keys. This is very convenient and makes it easy to get a nice plot 👍

A choroplethmapbox trace seems to not support this, and thus requires specifying any geometries as a manual GeoJSON file. It would be nice if choroplethmapbox supported the same automatic "inference" of appropriate geometries too.

Related issues:

• Introducing choroplethmapbox traces #3988 mentions the possibility of this, but it seems there's no progress:

  locationmode. The current behavior would correspond to locationmode: 'geojson-id'. Some users might expect to identify GeoJSON features using their properties.name (this would correspond to e.g. locationmode: 'geojson-prop-name'. Moreover, we could also support the locationmode values found in geo traces: 'ISO-3', 'USA-states', 'country names'

• Add new choroplethmapbox locationmode for geojson properties.id #4154 was, I think, about generalising the GeoJSON support in choroplethmapbox, but not adding the no-GeoJSON mode as here

• Add support for custom geojson polygons in choropleth traces #4267 was the opposite, I think: adding support for GeoJSON to choropleth

[gvwilson]

Hi - we are trying to tidy up the stale issues and PRs in Plotly's public repositories so that we can focus on things that are still important to our community. Since this one has been sitting for several years, I'm going to close it; if it is still a concern, please add a comment letting us know what recent version of our software you've checked it with so that I can reopen it and add it to our backlog. Thanks for your help - @gvwilson