diff --git a/game/theater/landmap.py b/game/theater/landmap.py
index 89dcdcf7..c5b422ad 100644
--- a/game/theater/landmap.py
+++ b/game/theater/landmap.py
@@ -1,5 +1,6 @@
 from dataclasses import dataclass
 import pickle
+from functools import cached_property
 from typing import Optional, Tuple, Union
 import logging
 
@@ -13,6 +14,18 @@ class Landmap:
     exclusion_zones: MultiPolygon
     sea_zones: MultiPolygon
 
+    def __post_init__(self):
+        if not self.inclusion_zones.is_valid:
+            raise RuntimeError("Inclusion zones not valid")
+        if not self.exclusion_zones.is_valid:
+            raise RuntimeError("Exclusion zones not valid")
+        if not self.sea_zones.is_valid:
+            raise RuntimeError("Sea zones not valid")
+
+    @cached_property
+    def inclusion_zone_only(self) -> MultiPolygon:
+        return self.inclusion_zones - self.exclusion_zones - self.sea_zones
+
 
 def load_landmap(filename: str) -> Optional[Landmap]:
     try:
diff --git a/gen/conflictgen.py b/gen/conflictgen.py
index d2bedfbe..b050e028 100644
--- a/gen/conflictgen.py
+++ b/gen/conflictgen.py
@@ -93,7 +93,7 @@ class Conflict:
         line = LineString([p0, p1])
 
         intersection = line.intersection(
-            theater.landmap.inclusion_zones.boundary)
+            theater.landmap.inclusion_zone_only.boundary)
         if intersection.is_empty:
             # Max extent does not intersect with the boundary of the inclusion
             # zone, so the full front line is usable. This does assume that the
diff --git a/resources/caulandmap.p b/resources/caulandmap.p
index 7ceefc71..c5076169 100644
Binary files a/resources/caulandmap.p and b/resources/caulandmap.p differ
diff --git a/resources/channellandmap.p b/resources/channellandmap.p
index 6ee32087..92864e8c 100644
Binary files a/resources/channellandmap.p and b/resources/channellandmap.p differ
diff --git a/resources/gulflandmap.p b/resources/gulflandmap.p
index a521f5e5..98fe5bce 100644
Binary files a/resources/gulflandmap.p and b/resources/gulflandmap.p differ
diff --git a/resources/nevlandmap.p b/resources/nevlandmap.p
index 42e34c37..f8ef5cbb 100644
Binary files a/resources/nevlandmap.p and b/resources/nevlandmap.p differ
diff --git a/resources/normandylandmap.p b/resources/normandylandmap.p
index 2d7ade8e..20eb8715 100644
Binary files a/resources/normandylandmap.p and b/resources/normandylandmap.p differ
diff --git a/resources/syrialandmap.p b/resources/syrialandmap.p
index 0d11a3c2..f39fb3bb 100644
Binary files a/resources/syrialandmap.p and b/resources/syrialandmap.p differ
diff --git a/resources/tools/generate_landmap.py b/resources/tools/generate_landmap.py
index 7e1a9f4b..a23c7fd1 100644
--- a/resources/tools/generate_landmap.py
+++ b/resources/tools/generate_landmap.py
@@ -1,11 +1,37 @@
 import pickle
+from functools import singledispatch
 
 from dcs.mission import Mission
-from shapely import geometry
-from shapely.geometry import MultiPolygon
+from shapely.geometry import GeometryCollection, MultiPolygon, Polygon
+from shapely.ops import unary_union
 
 from game.theater.landmap import Landmap
 
+
+@singledispatch
+def to_multipoly(obj) -> MultiPolygon:
+    raise NotImplementedError(
+        f"to_multipoly not implemented for {obj.__class__.__name__}")
+
+
+@to_multipoly.register
+def _poly_to_multipoly(obj: Polygon) -> MultiPolygon:
+    return MultiPolygon([obj])
+
+
+@to_multipoly.register
+def _multipoly_to_multipoly(obj: MultiPolygon) -> MultiPolygon:
+    return obj
+
+
+@to_multipoly.register
+def _geometry_collection_to_multipoly(obj: GeometryCollection) -> MultiPolygon:
+    if obj.is_empty:
+        return MultiPolygon()
+    raise RuntimeError(
+        f"Not sure how to convert collection to multipoly: {obj.wkt}")
+
+
 for terrain in ["cau", "nev", "syria", "channel", "normandy", "gulf"]:
     print("Terrain " + terrain)
     m = Mission()
@@ -19,19 +45,22 @@ for terrain in ["cau", "nev", "syria", "channel", "normandy", "gulf"]:
 
         if terrain == "cau" and inclusion_zones:
             # legacy
-            exclusion_zones.append(geometry.Polygon(zone))
+            exclusion_zones.append(Polygon(zone))
         else:
+            poly = Polygon(zone)
+            if not poly.is_valid:
+                raise RuntimeError(f"{plane_group} is invalid")
             if plane_group.units[0].type == "F-15C":
-                exclusion_zones.append(geometry.Polygon(zone))
+                exclusion_zones.append(poly)
             else:
-                inclusion_zones.append(geometry.Polygon(zone))
+                inclusion_zones.append(poly)
 
     for ship_group in m.country("USA").ship_group:
         zone = [(x.position.x, x.position.y) for x in ship_group.points]
-        seas_zones.append(geometry.Polygon(zone))
+        seas_zones.append(Polygon(zone))
 
     with open("../{}landmap.p".format(terrain), "wb") as f:
         print(len(inclusion_zones), len(exclusion_zones), len(seas_zones))
-        pickle.dump(Landmap(MultiPolygon(inclusion_zones),
-                            MultiPolygon(exclusion_zones),
-                            MultiPolygon(seas_zones)), f)
+        pickle.dump(Landmap(to_multipoly(unary_union(inclusion_zones)),
+                            to_multipoly(unary_union(exclusion_zones)),
+                            to_multipoly(unary_union(seas_zones))), f)