Initial public release

docs/specs/GIS_STANDARDS.md

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+# 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.