crs-l1-london-laea-areas

Analyst notes

Description

Tests whether the agent recognizes that computing area on WGS84 (degree) geometries is meaningless, and reprojects to an equal-area CRS before measuring. The prompt deliberately omits any CRS hint, so the agent has to spot the problem from the input metadata.

Approach

1. Read `london_admin.geojson` and inspect its CRS metadata.
2. Recognize the geometries are in WGS84, so area measured directly would come out in degrees² and be meaningless.
3. Pick an equal-area projection appropriate for Europe. LAEA Europe (EPSG:3035) is the canonical choice.
4. Reproject the polygons and compute their area in square metres.
5. Convert to square kilometres and write a CSV with columns id, name, area_km2.

Pitfalls

• Calling `.area` directly on WGS84 geometries gives a result in degrees², not metres².
• Picking a single-zone projection (like a UTM zone) for a region that spans several zones throws the totals off.
• Forgetting the m² → km² conversion leaves the numbers off by a factor of a million.
• Filtering to just the 33 borough-level `county` features and dropping the `locality` rows cuts the output to 33 of 232 rows, which a real run did before the prompt spelled out both subtypes.
• Dropping or renaming the id and name columns breaks the join back to the original admin units.

Recent runs task v5