Max zoom level no longer working from 0.14.0 to 0.15.1 (defaults to 18)

[Stéphane]

Describe the bug
Since the update from 0.14.0 to 0.15.1, the max zoom level function does no longer work and defaults to 18?

To Reproduce

[ Include a code snippet that produces your bug. Make it standalone, we should be able to run it. ]

import folium
m = folium.Map(location=[51.505492, -0.075408], zoom_start=12, max_zoom=25)
# add a circle marker of 5 radius at scale at the center of the map
folium.CircleMarker(location=[51.505492, -0.075408], radius=5, color='#3186cc', fill=True, fill_color='#3186cc').add_to(m)
m.save('interactive_map_0.14.0.html')

[ Include a data sample or link to your data if necessary to run the code ]

Expected behavior
I expect the maximum zoom level to be 25 instead of 18

Environment (please complete the following information):

maps.zip

Possible solutions
List any solutions you may have come up with.

folium is maintained by volunteers. Can you help making a fix for this issue?

[Frank Anema]

Can confirm. In the TileLayer class we now default to the max_zoom that's defined in the xyzservices.TileProvider object if available.

Also note how this works in tandem with max_native_zoom.

We should fix this and improve documentation.

[Stéphane]

So there is still a possibility to increase the zoom level? Or is it disabled in the newest updates? If you are working on a small scale (e.g. meters), this is almost a necessity.

[Hans Then]

@Stephaneke The maximum zoom is defined by the tile provider. You can play around with different tile layers to see how that affects the max zoom level. E.g. folium.TileLayer('CartoDB Positron').add_to(m) gives me a maximum zoom level of 20. OpenStreetMap (the default) goes to 19.

Our documentation is off as the max_zoom and max_native_zoom parameters seem to be ignored.

[Hans Then]

@Stephaneke I did a quick experiment with a different provider. This one goes to level 22, which is the best I could find. It does require an api key. Parts in angle brackets need to be replaced.

See https://github.com/leaflet-extras/leaflet-providers/blob/master/leaflet-providers.js for other providers.

folium.TileLayer(
     'https://tile.jawg.io/<variant, e.g. jawg-dark>/{z}/{x}/{y}{r}.png?access-token=<get your own>',
      attr="<attribution>",
      max_zoom=22,
      max_native_zoom=22,
  ).add_to(m)

[Frank Anema]

This probably broke when we adopted xyzservices. This probably needs more than just a documentation change. Ideally we restore the previous behavior as described in the rasterlayer docstring. But now the ‘max_native_zoom’ value comes from xyzservices? And ‘max_zoom’ allows further zooming? Something like that.

[Hans Then]

I did a few tests. max_zoom on Map does not seem to be honored at all and leaflet seems to be taking the max zoom level from the tile layers. max_native_zoom on TileLayer seems to do nothing (probably because it comes from xyzservice). max_zoom on TileLayer does seem to limit how far you can zoom in for that TileLayer. Leaflet will fall back to the default TileLayer if you zoom in beyond that.

My feeling is that max_zoom on Map should just limit how far one can zoom if it is less than the maximum zoom level of the associated layers. Perhaps we can give a warning if the user sets a too high max_zoom level?

[Frank Anema]

I made a PR to bring back the behavior we had before, while keeping the values we get from xyzservices: #1952