fix: clarify population evolution semantics

backend/app/services/vector_feature_service.py

@@ -209,8 +209,8 @@ class VectorFeatureService:
                 intersection_area = func.ST_Area(
                     func.ST_Transform(func.ST_Intersection(VectorFeature.geometry, envelope), 31370)
                 )
-                value_expression = numeric_value * intersection_area / func.nullif(source_area, 0.0)
-                is_estimate = True
+                coverage_ratio = intersection_area / func.nullif(source_area, 0.0)
+                value_expression = numeric_value * coverage_ratio
             aggregate_value = (
                 db.query(func.coalesce(func.sum(value_expression), 0.0))
                 .filter(*selection_filter)
@@ -218,6 +218,16 @@ class VectorFeatureService:
                 .scalar()
             )
             metric_value = float(aggregate_value or 0.0)
+            if method == "area_weighted_sum":
+                partial_feature_count = (
+                    db.query(func.count(VectorFeature.id))
+                    .filter(*selection_filter)
+                    .filter(coverage_ratio < 0.999999)
+                    .scalar()
+                )
+                is_estimate = bool(partial_feature_count)
+                if not is_estimate and config.get("warning_only_when_estimate", True):
+                    warning = None
         elif method != "feature_count":
             raise AppError(
                 code="INVALID_SELECTION_AGGREGATION",