Map tiles: switch to Esri World Light Gray (OSM 403s file://)

tiles="OpenStreetMap" returned HTTP 403 "referer is required by tile usage
policy" in the target browser — OSM graylists refererless requests and a
karte.html opened via file:// sends no Referer. Esri's Canvas/World_Light_Gray
base + reference layers need neither a key nor a Referer and keep the muted
look. New MAP_TILES / MAP_TILES_LABELS / MAP_TILES_ATTR constants; generate_map
adds them as explicit TileLayers.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/architecture.md

@@ -112,6 +112,6 @@ This is the file to ask for when diagnosing a problem on the user's laptop.
 |------------|-----------|-------------------|
 | Nominatim (OSM) | geocoding new/edited entries | entries save with blank coords, shown as `⚠ nicht gefunden` |
 | CDN (jsdelivr, jquery, cloudflare) | rendering `karte.html` | map page loads blank / unstyled |
-| OpenStreetMap tiles (`tile.openstreetmap.org`) | map background | blank/grey tiles |
+| Esri tiles (`server.arcgisonline.com`) | map background | blank/grey tiles |
 
 Existing entries that already have coordinates do **not** need the network.

docs/changelog.md

@@ -2,6 +2,16 @@
 
 Notable changes to the app. Newest first.
 
+## 2026-09-07 — map tiles → Esri (OSM 403s local files)
+
+The switch to `tiles="OpenStreetMap"` worked on the dev machine but the target
+laptop's browser got **HTTP 403 "referer is required by tile usage policy"** —
+OSM's CDN blocks refererless requests, and a `karte.html` opened as `file://`
+sends no `Referer`. Switched to **Esri "World Light Gray"** (base + labels
+overlay, `server.arcgisonline.com`): no key, no `Referer` check, muted look
+similar to the old positron. Constants `MAP_TILES` / `MAP_TILES_LABELS` /
+`MAP_TILES_ATTR`.
+
 ## 2026-09-07 — install split for non-admin users
 
 The target account has no sudo, so install is two scripts:

docs/dev-notes.md

@@ -36,19 +36,26 @@ Numeric parsing is deliberately deferred to `get_map_data` (`pd.to_numeric(...,
 errors="coerce")`). Don't "fix" columns to float on load — blank coordinates and
 leading-zero PLZ both depend on the string representation.
 
-## CartoDB "positron" tiles now require an API key (2026-09-07)
+## Map tiles: Carto needs a key, OSM 403s file:// — use Esri (2026-09-07)
 
-The original `folium.Map(tiles="CartoDB positron")` started rendering an
-"API KEY REQUIRED / carto.com/basemaps/apikey" watermark – Carto moved its
-basemaps behind a key. Switched to `tiles="OpenStreetMap"` (constant
-`MAP_TILES`), which needs no key. Trade-off: OSM standard tiles are more
-colourful than positron's muted grey. Other no-key options if a lighter look is
-wanted: OSM Germany (`tile.openstreetmap.de`), OSM France Hot
-(`{s}.tile.openstreetmap.fr/hot`) – both still colourful. Truly muted
-key-free basemaps are hard to find now.
+Two dead ends before landing on Esri:
 
-Don't assume a "free" third-party tile source stays free – pin the provider in
-one constant so swapping it is a one-line change.
+1. `folium.Map(tiles="CartoDB positron")` → "API KEY REQUIRED" watermark; Carto
+   moved basemaps behind a key.
+2. `tiles="OpenStreetMap"` → worked in `curl` from the dev machine but the
+   **user's browser got HTTP 403 "referer is required by tile usage policy"**.
+   OSM's tile CDN graylists refererless requests, and a `karte.html` opened as a
+   local `file://` sends no `Referer`. A browser can't add one. Dead end for
+   this app's "open a local HTML file" model.
+
+Now: **Esri "World Light Gray"** base + reference (labels) overlay
+(`server.arcgisonline.com/ArcGIS/rest/services/Canvas/…`). No key, no `Referer`
+check, light/muted look close to the old positron. `MAP_TILES` /
+`MAP_TILES_LABELS` constants; comment lists Esri Street/Topo as swaps.
+
+Lesson: a tile source that works from `curl` or an `http://` page can still fail
+from `file://`. Test the map by **opening the generated `karte.html` directly**,
+not just by checking the URL in the HTML.
 
 ## Nominatim query order matters
 

docs/improvements.md

@@ -163,11 +163,11 @@ or at least skip exact duplicates by default.
 ## 9. Offline map 🟢
 
 `karte.html` loads Leaflet/jQuery/Bootstrap from CDNs and tiles from
-`tile.openstreetmap.org` (`MAP_TILES`; switched away from CartoDB positron, which
-now needs an API key). The map is blank without internet even though all the
-data is local. If offline use matters, vendor the Leaflet JS/CSS into `data/`
-and post-process the Folium output to point at local files (tiles would still
-need caching or an offline tile pack — larger effort).
+`server.arcgisonline.com` (Esri; `MAP_TILES` — Carto needs a key, OSM 403s
+`file://`). The map is blank without internet even though all the data is local.
+If offline use matters, vendor the Leaflet JS/CSS into `data/` and post-process
+the Folium output to point at local files (tiles would still need caching or an
+offline tile pack — larger effort).
 
 ## 10. Small code-quality items 🟢 — partly done
 

docs/overview.md

@@ -65,9 +65,10 @@ A table view of everything in `orte.csv`.
 
 Generated by `generate_map()`:
 
-- Base layer: **OpenStreetMap** standard tiles (`MAP_TILES`) – no API key.
-  Initial view centred on `[49.0, 9.0]`, zoom 8 (roughly Baden-Württemberg);
-  the view auto-fits to the markers when there is more than one.
+- Base layer: **Esri "World Light Gray"** (`MAP_TILES` + a labels overlay) – a
+  light, muted basemap that needs no API key and no `Referer`. Initial view
+  centred on `[49.0, 9.0]`, zoom 8; auto-fits to the markers when there is more
+  than one.
 - One **`CircleMarker`** per unique `(city, lat, lon)` group. Radius scales
   linearly with the visit count for that location
   (`5 + count / max_count * 20` px), colour is DRK red (`#CC0000`).
@@ -77,11 +78,12 @@ Generated by `generate_map()`:
   bar shows a warning).
 
 > The generated HTML pulls Leaflet, jQuery and Bootstrap from CDNs, and the map
-> tiles from `tile.openstreetmap.org`, so the map needs an internet connection to
-> render even though the data is local. To change the look, set `MAP_TILES` near
-> the top of `app.py` to another no-key provider Folium knows
-> (`"OpenStreetMap"`, `"CartoDB positron"` *now needs a key*, or a custom
-> `folium.TileLayer` URL such as OSM Germany / OSM France).
+> tiles from `server.arcgisonline.com`, so the map needs an internet connection
+> to render even though the data is local. To change the look, edit `MAP_TILES` /
+> `MAP_TILES_LABELS` near the top of `app.py` — the comment there lists other
+> no-key Esri layers (Street, Topo). `tile.openstreetmap.org` was tried first
+> but its tile-usage policy **403s** pages opened from `file://` (no `Referer`);
+> `CartoDB positron` needs an API key.
 
 ## Geocoding behaviour