Measurement company Podtrac has released Top Podcasts By Country, which lists the single #1 podcast in each of 48 countries. (The inaugural list, covered by RAIN HERE, ranked only 30 countries.)
The chart which delivers these results (see it HERE) reveals the publisher of each top podcast, and the topical category. The chart is pleasingly interactive, so clicking on any column header re-sorts the entire thing alphabetically within that column.
While some Podtrac rankers show only Podtrac-measured shows, this list includes podcasts measured elsewhere. Podrac discloses that the results for those shows are estimated, but does not offer details of the estimation process.
However, scrolling down the page does give a fair amount of detail about different ranking methods. That piece of the puzzle is HERE.