# 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.