diff --git a/planetiler-custommap/src/main/resources/samples/shortbread.spec.yml b/planetiler-custommap/src/main/resources/samples/shortbread.spec.yml
index 69452963..c238037b 100644
--- a/planetiler-custommap/src/main/resources/samples/shortbread.spec.yml
+++ b/planetiler-custommap/src/main/resources/samples/shortbread.spec.yml
@@ -39,7 +39,7 @@ examples:
 - name: waterway=dock
   input:
     source: osm
-    geometry: polygon
+    geometry: POLYGON ((-0.5 -0.5, 0.5 -0.5, 0.5 0.5, -0.5 0.5, -0.5 -0.5))
     tags:
       waterway: dock
   output:
@@ -48,6 +48,11 @@ examples:
     min_zoom: 10
     tags:
       kind: dock
+      # verified with a naive "projection" and sizes from https://www.thoughtco.com/degree-of-latitude-and-longitude-distance-4070616
+      # 1° lat ~ 110.567km at the equator
+      # 1° lon ~ 111.321km at the equator
+      # => ~12308.429km² = ~12308.429e^6 m² = ~1.2308429e^10 m²
+      way_area: 1.236418893560872E10
 
 - name: waterway=canal linestring
   input:
diff --git a/planetiler-custommap/src/main/resources/samples/shortbread.yml b/planetiler-custommap/src/main/resources/samples/shortbread.yml
index c7776bba..c4267248 100644
--- a/planetiler-custommap/src/main/resources/samples/shortbread.yml
+++ b/planetiler-custommap/src/main/resources/samples/shortbread.yml
@@ -63,6 +63,8 @@ layers:
     attributes:
     - key: kind
       type: match_value
+    - key: way_area # area in square meter (Mercator Projection)
+      value: "${ feature.area('m2') }"
 
 - id: water_polygons_labels
   features:
@@ -80,6 +82,8 @@ layers:
     - *name
     - *name_en
     - *name_de
+    - key: way_area # area in square meter (Mercator Projection)
+      value: "${ feature.area('m2') }"
 
 - id: water_lines
   features: