geointel/docs/18-ultra-prep/GEOMETRY_CONTRACTS.md

Geometry Contracts

Internal Geometry Standard

• Database geometries are stored in PostGIS.
• Default storage CRS: EPSG:31370 for Belgian projected operations where appropriate, or EPSG:4326 for API interchange.
• API GeoJSON is always EPSG:4326 unless explicitly stated.
• Area calculations must use projected CRS, not raw WGS84 degrees.

Accepted Area Input

• GeoJSON Polygon
• GeoJSON MultiPolygon
• drawn polygon from frontend
• future: municipality selection

Validation Rules

• polygon must be closed;
• polygon must be valid;
• polygon must have non-zero area;
• self-intersections must be rejected or repaired explicitly;
• extremely large areas must require confirmation or be rejected by configured max area.

Output Rules

• include crs metadata if transformed;
• include computed area in square meters;
• include bounds;
• include geometry validity status.

Common Trap

Never compute area or distance in degrees.