diff --git a/backend/app/services/cadastre/grid_geometry.py b/backend/app/services/cadastre/grid_geometry.py
index 1c1d8728..40c4cb7c 100644
--- a/backend/app/services/cadastre/grid_geometry.py
+++ b/backend/app/services/cadastre/grid_geometry.py
@@ -46,12 +46,28 @@ def quarter_bbox_3857(db: Session, quarter: str) -> tuple[float, float, float, f
     if not row or row["xmin"] is None:
         logger.warning("quarter_bbox_3857: квартал %s не найден в cad_quarters_geom", quarter)
         return None
-    return (
+    bbox = (
         float(row["xmin"]),
         float(row["ymin"]),
         float(row["xmax"]),
         float(row["ymax"]),
     )
+    # Sanity check: cad_quarters_geom имеет ~72% rows с broken micro-precision
+    # geometry (width <0.01m). Это вызывает useless 1px tiles в WMS и 500 errors
+    # от NSPD. Реальный квартал ЕКБ имеет width 200-4000м. Skip grid-walk для
+    # broken — snapshot phase даст 20 per cat, что норм для MVP.
+    width = bbox[2] - bbox[0]
+    height = bbox[3] - bbox[1]
+    if width < 100 or height < 100 or width > 10000 or height > 10000:
+        logger.warning(
+            "quarter_bbox_3857: квартал %s broken geom — width=%.2fm height=%.2fm "
+            "(expected 100-10000m). Grid-walk skipped, only snapshot phase.",
+            quarter,
+            width,
+            height,
+        )
+        return None
+    return bbox
 
 
 def generate_grid_click_points(