Index: trunk/styles/standard/elemstyles.mapcss
===================================================================
--- trunk/styles/standard/elemstyles.mapcss	(revision 9097)
+++ trunk/styles/standard/elemstyles.mapcss	(revision 9099)
@@ -4866,5 +4866,23 @@
 /*************/
 
+/* small extent for unclosed area (see below for closed) */
 area[setting("partial_fill")] {
+    fill-extent: 15;
+}
+
+/* Turn partial fill off and us plain fill, when the partial fill covers about
+   100% of the area. This reduces artifacts (typically for incomplete multipolygons).
+   Switching between full and partial fill while drawing an area might be irritating,
+   so only do this at low zoom. */
+area|z-13[setting("partial_fill")] {
+    fill-extent-threshold: 100%;
+}
+
+/* Larger extent for closed areas.
+   Turn partial fill off, when it covers more than about 70% of the area. This is avoids
+   areas with small unfilled patches in the center. */
+area[setting("partial_fill")]:closed2 {
     fill-extent: 25;
-}
+    fill-extent-threshold: 70%;
+}
+