Publicize _calculate_zoom

[martinfleis]

I think that contextily.tile._calculate_zoom should be part of a public API. It is useful if you want to fine-tune zoom levels, to know which one you start from. And it is also part of the intro guide. https://contextily.readthedocs.io/en/latest/intro_guide.html#Fine-tune-zoom-levels

[jorisvandenbossche]

+1 to make this easier in some way.

For me a potential downside of calculate zoom is that it requires (w, s, e, n)(but we could also improve the interface of course, eg accepting a geodataframe in different crs).
Another idea that I had at some point would be to add a verbose=True option to add_basemap (and other similar functions), which would eg print which zoom level is being used, so it's easier to set it slightly larger/smaller. Of course, that can only be used interactively, as it's not a function.

[darribas]

+1 Also, related, I've been using the new overlay feature and I find consistently that I end up going for the default value of zoom - 1 (one more zoomed out). Is this something you run into as well? If so, maybe we could change the 'auto' algorithm to have that as default?

[martinfleis]

I find consistently that I end up going for the default value of zoom - 1 (one more zoomed out). Is this something you run into as well?

I was changing the zoom level for overlay labels in about 50% of cases.