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Paddy e3bbd4d264 Switch map tiles from CartoDB positron to OpenStreetMap (no API key)

CartoDB's positron basemap now renders an "API KEY REQUIRED" watermark.
Use tiles="OpenStreetMap" via a new MAP_TILES constant instead.

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

2026-09-07 19:08:09 +02:00

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Dev notes — assumptions that turned out wrong

Running list so the same mistakes aren't repeated. Add to it whenever reality contradicts an assumption.

The macOS system Python can't run the GUI; use a Homebrew Python (2026-09-07)

The macOS CommandLineTools Python 3.9 (/Library/Developer/CommandLineTools/ .../python3.9) ships Tk 8.5.9. ttkbootstrap 1.10.1 requires Tk 8.6+. Symptoms: TclError: couldn't recognize image data (window icon) and TclError: unknown option "-style" on ttk.Scrollbar.

Fix for local GUI testing: brew install python-tk@3.12 (pulls tcl-tk, gives Python 3.12 + Tk 9.0), then:

/opt/homebrew/bin/python3.12 -m venv venv
venv/bin/pip install -r requirements.txt
venv/bin/python app.py

ttkbootstrap 1.10.1 runs fine on Tk 9.0 in practice (verified: window builds, Treeview sort, DateEntry, LabelFrame, custom styles all work).

The Linux Mint target uses its own python3-tk (Tk 8.6+) and is unaffected either way.
screencapture from a non-GUI shell fails ("could not create image from display") without Screen-Recording permission — automated screenshots of the running app aren't available here; verify by building the widget tree and driving it programmatically instead.

`pandas` reads everything as strings by design

DataStore._load uses dtype={...: str} for postal_code, lat, lon. 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)

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.

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.

Nominatim query order matters

geocode_city returns the first hit, trying PLZ-qualified first, then each region in GEOCODE_REGIONS, then a bare ", Germany". Reordering changes which coordinates ambiguous town names resolve to.

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