geointel/docs/specs/GIS_STANDARDS.md

GIS Standards

CRS standards

• API GeoJSON: EPSG:4326.
• Internal Belgian metric calculations: EPSG:31370.
• Raster native operations preserve source CRS unless reproject requested.
• Store both source CRS and normalized CRS.

Units

• Area: square meters internally, hectares/km² as display derivatives.
• Length: meters internally, kilometers as display derivative.
• Resolution: meters/pixel where projected CRS allows it; otherwise state units clearly.

Geometry validity

All vector geometries must pass validation before becoming READY.

Allowed repair strategies:

1. make_valid where available.
2. zero-width buffer only if documented.
3. reject and require user correction.

Repairs must be recorded in metadata.

Geometry type normalization

• Polygon inputs may become MultiPolygon.
• LineString inputs may become MultiLineString.
• GeometryCollections require explicit extraction or rejection.

Spatial operations

All spatial operations must define:

• input CRS;
• output CRS;
• unit assumptions;
• tolerance;
• geometry repair behavior;
• empty-result behavior.

Precision

Store full precision in database. Simplify only derived visualization layers.

Boundary handling

For clipping/intersections, include features that intersect area boundary. Record whether metrics use full feature geometry or clipped geometry.

Source priority for V1 reference workflows

1. GRB-like reference fixtures / GRB when implemented.
2. Official Flemish datasets where available.
3. OSM fallback.
4. User-uploaded reference layer.