Map output from OSM returns blocked tiles, due to defective request or not following referer-policy

[joncto]

Bug description
I am plotting a data set to be projected on a map, using Folium. However, the default OSM representation doesn't work properly.

The map renders as this, displaying a lot of warnings on 403 errors:

Reading the OSM wiki page about Blocked tiles, one might assume that Folium currently doesn't comply to OSM's policies?

To Reproduce
Code excerpt:

import folium

# convert to pandas dataframe
import pandas as pd
df = pd.DataFrame(folkegrupper, columns=["Historic name", "Modern name", "English name", "Area", "Longitude", "Latitude"])

# create map
m = folium.Map(location=[30, 70], zoom_start=3)

# add points to map
for index, row in df.iterrows():
    folium.CircleMarker(
        location=[row["Longitude"], row["Latitude"]],
        radius=15,
        color="blue",
        fill=True,
        fill_color="blue",
        fill_opacity=0.6,
        tooltip=f"Modern name: {row['Modern name']}",
        popup=f"Historic name: {row['Historic hame']}<br>Area: {row['Area']}"
    ).add_to(m)

# display map
m

Example data for testing code above (variable must be run before the code)

folkegrupper = [
    ("group1a", "group1b", "group1c", "Sør-Afrika", -30.0550, 23.6235),
    ("group2a", "group2b", "group2c", "Malaysia", 4.2105, 101.6864),
    ("group3a", "group3b", "group3c", "Nord-Russland", 59.4372, 105.3305),
    ("group4a", "group4b", "group4c", "Midtøsten", 27.2750, 49.8718),
    ("group5a", "group5b", "group5c", "India", 20.5937, 78.9629),
    ("group6a", "group6b", "group6c", "Verden", 0, 0),
    ("group7a", "group7b", "group7c", "Sør-Afrika", -25.7302, 28.2092)
]

Expected behavior
GIVEN valid code and a dataset with geodata,
WHEN the code is run,
THEN an interactive map should display without blocked tiles

Environment info

• Browser: Firefox 151.0.3 (used to display html output)
• Python version: 3.12.13
• folium version: 0.20.0

[Otavio-Novais]

Hi everyone!

I've been exploring the project recently and wanted to look into this issue as a way to get started. After looking into how referrerPolicy is handled, here is what I found:

Folium successfully passes Leaflet's referrerPolicy to the tile layer, so the package functionality is working as intended. However, the 403 Forbidden error from OpenStreetMap happens when the generated HTML map is opened directly from the local disk (file:// protocol), especially in browsers like Firefox.

In these cases, the browser security policy restricts or completely omits the standard HTTP Referer header for local files. Since OpenStreetMap's tile policy strictly requires a valid Referer, the server rejects the request.

It looks like this is a browser/origin limitation regarding local files rather than a rendering bug in Folium. For anyone encountering this, a reliable workaround is to serve the generated HTML file over a local HTTP server (for example, by running python -m http.server in the directory) or to use a tile source that doesn't enforce strict Referer checks.

Let me know if I missed anything or if there's any other way I can help!

[hansthen]

This is a duplicate of #2215. As @Otavio-Novais notes, this is out of our control. This is caused by a combination of browser policies and OSM tile policy, neither of which are part of Folium.