How are admin level 6 boundaries missing from OSM rendered in geoBoundaries ADM2?

[ksmithNau]

I would like to know how you rendered the complete looking image of OSM ADM2 and what the source of this is.

OSM-Boundaries dataset does not use ADM0-2 and OSM source appears to be missing entire counties at admin level 6 for many countries (Japan, Saudi Arabia, Thailand, Turkey, etc.). I understand that the ADM2 and OSM Admin Level 6 aren't a one-to-one comparison, which drives my question of how you're rendering ADM2 from OSM.

How are you rendering polygons that are missing from the underlying datasets? How can I query/extract what is being rendered?

geoBoundaries UI for Japan OSM-Boundaries ADM2:

OSM-Boundaries UI for Japan Admin 5 & 6:

OSM Raw Extract for Japan Admin Level 6:

In my workflow, I initially thought this was an issue with Overture Maps dataset, but discovered the upstream issue is in OSM.

[DanRunfola]

One of our former (graduated) Ph.D. students - Dr. Bahgat - was the one that worked on those pipelines, which can be found (I think) here:
https://github.com/wmgeolab/geoContrast

@karimbahgat any information you can provide on this one? I'm not sure the exact crosswalk you used for OSM.

[ksmithNau]

@DanRunfola thanks for the pointer.

Sort of unrelated to this discussion topic, but something I realized in my workflow comparing OSM admin level 6 and geoBoundaries ADM2, the global ADM2 polygons have significantly lower vertex count than the individual country polygons. Is that what was meant by extensive simplification for the CGAZ downloads? If I download all the individual country files at ADM2 and try to merge them, will there be overlap with the national boundaries?

[DanRunfola]

If you're referring to the CGAZ ADM2, then - yes, you will see extensive simplification. The individual polygons will have much higher vertex counts, but will overlap in many cases.