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name: geojson-and-data description: "Render GeoJSON, TopoJSON, and choropleths in Folium with stable identifiers, correct coordinate order, and validated data bindings." disable-model-invocation: true metadata: disco-role: operating license: NOASSERTION

GeoJSON and data

Use this sub-skill when you need Folium's geospatial data surfaces: GeoJson, TopoJson, Choropleth, GeoJsonTooltip, GeoJsonPopup, ClickForMarker, ClickForLatLng, or JsCode callbacks tied to GeoJson.

Use when

• the input is GeoJSON, TopoJSON, a __geo_interface__ object, or a GeoPandas GeoDataFrame
• tabular values must be joined to shapes for a choropleth
• feature-level styling, highlighting, tooltips, popups, or JavaScript callbacks are needed
• point geometries need marker=... customization inside GeoJson
• coordinate-order issues or missing identifiers need render-time diagnosis

Route elsewhere

• base maps, tile selection, layer composition, and non-GeoJSON overlays -> ../map-and-layers/SKILL.md
• Search, Timeline, TimestampedGeoJson, Realtime, VectorGrid, and similar plugin workflows -> ../plugins/SKILL.md
• upstream GIS cleaning, topology repair, or CRS surgery beyond Folium's render contract -> keep that upstream

Working order

1. Normalize the input form and confirm the geometry surface.
2. Check coordinate order: Folium map and marker inputs are [lat, lon]; GeoJSON coordinates are [lon, lat].
3. Choose GeoJson, TopoJson, or Choropleth.
4. Decide the join key (id, properties.*, or key_on) before styling.
5. Attach GeoJsonTooltip and GeoJsonPopup only after confirming the property fields exist.
6. Use JsCode for on_each_feature when Python callbacks are not enough.
7. Validate missing values, bins, and legend behavior before handoff.

Bundled references

• Data formats and input contracts
• Workflow recipes
• Troubleshooting

Bundled script

• render_geojson_choropleth.py — tiny no-network smoke test for GeoJSON/choropleth binding, with optional --geojson, --csv, and --output.

Quick reminders

• GeoJson accepts dicts, JSON strings, file paths, URLs, and objects with __geo_interface__; if to_crs exists, Folium reprojects to EPSG:4326 before rendering.
• TopoJson needs an object path such as objects.counties.
• Choropleth expects table keys to match key_on; bins can be an integer or an explicit edge list.
• ClickForMarker and ClickForLatLng are map helpers, not GeoJson.marker types.
• For loop-built style_functions, bind loop variables early (style=style) to avoid late-binding closure bugs.
• If embed=False, keep the source as a URL or file path and provide data that can already behave as a FeatureCollection for styling.
• ClickForLatLng is useful when diagnosing swapped coordinate order because it reports clicked map coordinates in Folium's [lat, lon] order.