diff --git a/MapControl/Shared/AzimuthalEquidistantProjection.cs b/MapControl/Shared/AzimuthalEquidistantProjection.cs
index 5a1eb738..52027047 100644
--- a/MapControl/Shared/AzimuthalEquidistantProjection.cs
+++ b/MapControl/Shared/AzimuthalEquidistantProjection.cs
@@ -36,7 +36,7 @@ namespace MapControl
 
             Center.GetAzimuthDistance(latitude, longitude, out double azimuth, out double distance);
 
-            var mapDistance = distance * Wgs84EquatorialRadius;
+            var mapDistance = distance * Wgs84MeanRadius;
 
             return new Point(mapDistance * Math.Sin(azimuth), mapDistance * Math.Cos(azimuth));
         }
@@ -50,7 +50,7 @@ namespace MapControl
 
             var azimuth = Math.Atan2(x, y);
             var mapDistance = Math.Sqrt(x * x + y * y);
-            var distance = mapDistance / Wgs84EquatorialRadius;
+            var distance = mapDistance / Wgs84MeanRadius;
 
             return Center.GetLocation(azimuth, distance);
         }
diff --git a/MapControl/Shared/GnomonicProjection.cs b/MapControl/Shared/GnomonicProjection.cs
index 44699cbc..5013e35c 100644
--- a/MapControl/Shared/GnomonicProjection.cs
+++ b/MapControl/Shared/GnomonicProjection.cs
@@ -37,7 +37,7 @@ namespace MapControl
             Center.GetAzimuthDistance(latitude, longitude, out double azimuth, out double distance);
 
             var mapDistance = distance < Math.PI / 2d
-                ? Math.Tan(distance) * Wgs84EquatorialRadius
+                ? Math.Tan(distance) * Wgs84MeanRadius
                 : double.PositiveInfinity;
 
             return new Point(mapDistance * Math.Sin(azimuth), mapDistance * Math.Cos(azimuth));
@@ -52,7 +52,7 @@ namespace MapControl
 
             var azimuth = Math.Atan2(x, y);
             var mapDistance = Math.Sqrt(x * x + y * y);
-            var distance = Math.Atan(mapDistance / Wgs84EquatorialRadius);
+            var distance = Math.Atan(mapDistance / Wgs84MeanRadius);
 
             return Center.GetLocation(azimuth, distance);
         }
diff --git a/MapControl/Shared/Location.cs b/MapControl/Shared/Location.cs
index 143db6ab..74f1a47a 100644
--- a/MapControl/Shared/Location.cs
+++ b/MapControl/Shared/Location.cs
@@ -115,7 +115,7 @@ namespace MapControl
         /// <summary>
         /// Calculates the great circle distance in meters between this and the specified Location.
         /// </summary>
-        public double GetDistance(Location location, double earthRadius = MapProjection.Wgs84EquatorialRadius)
+        public double GetDistance(Location location, double earthRadius = MapProjection.Wgs84MeanRadius)
         {
             GetAzimuthDistance(location.Latitude, location.Longitude, out _, out double distance);
 
@@ -144,7 +144,7 @@ namespace MapControl
         /// <summary>
         /// Calculates the Location on a great circle at the specified azimuth in degrees and distance in meters from this Location.
         /// </summary>
-        public Location GetLocation(double azimuth, double distance, double earthRadius = MapProjection.Wgs84EquatorialRadius)
+        public Location GetLocation(double azimuth, double distance, double earthRadius = MapProjection.Wgs84MeanRadius)
         {
             return GetLocation(azimuth * Math.PI / 180d, distance / earthRadius);
         }
diff --git a/MapControl/Shared/MapProjection.cs b/MapControl/Shared/MapProjection.cs
index 8cb106bb..1bd8856e 100644
--- a/MapControl/Shared/MapProjection.cs
+++ b/MapControl/Shared/MapProjection.cs
@@ -29,7 +29,11 @@ namespace MapControl
         public const double Wgs84EquatorialRadius = 6378137d;
         public const double Wgs84MeterPerDegree = Wgs84EquatorialRadius * Math.PI / 180d;
         public const double Wgs84Flattening = 1d / 298.257223563;
-        public static readonly double Wgs84Eccentricity = Math.Sqrt((2d - Wgs84Flattening) * Wgs84Flattening);
+
+        // Arithmetic mean radius (2*a + b) / 3 == (1 - f/3) * a
+        // https://en.wikipedia.org/wiki/Earth_radius#Arithmetic_mean_radius
+        //
+        public const double Wgs84MeanRadius = (1d - Wgs84Flattening / 3d) * Wgs84EquatorialRadius;
 
         public static MapProjectionFactory Factory
         {
diff --git a/MapControl/Shared/OrthographicProjection.cs b/MapControl/Shared/OrthographicProjection.cs
index 4623fcf4..3a764ef5 100644
--- a/MapControl/Shared/OrthographicProjection.cs
+++ b/MapControl/Shared/OrthographicProjection.cs
@@ -44,8 +44,8 @@ namespace MapControl
             }
 
             return new Point(
-                Wgs84EquatorialRadius * Math.Cos(lat) * Math.Sin(dLon),
-                Wgs84EquatorialRadius * (Math.Cos(lat0) * Math.Sin(lat) - Math.Sin(lat0) * Math.Cos(lat) * Math.Cos(dLon)));
+                Wgs84MeanRadius * Math.Cos(lat) * Math.Sin(dLon),
+                Wgs84MeanRadius * (Math.Cos(lat0) * Math.Sin(lat) - Math.Sin(lat0) * Math.Cos(lat) * Math.Cos(dLon)));
         }
 
         public override Location MapToLocation(double x, double y)
@@ -55,8 +55,8 @@ namespace MapControl
                 return new Location(Center.Latitude, Center.Longitude);
             }
 
-            x /= Wgs84EquatorialRadius;
-            y /= Wgs84EquatorialRadius;
+            x /= Wgs84MeanRadius;
+            y /= Wgs84MeanRadius;
             var r2 = x * x + y * y;
 
             if (r2 > 1d)
diff --git a/MapControl/Shared/StereographicProjection.cs b/MapControl/Shared/StereographicProjection.cs
index d4a3719b..ef3e396d 100644
--- a/MapControl/Shared/StereographicProjection.cs
+++ b/MapControl/Shared/StereographicProjection.cs
@@ -36,7 +36,7 @@ namespace MapControl
 
             Center.GetAzimuthDistance(latitude, longitude, out double azimuth, out double distance);
 
-            var mapDistance = Math.Tan(distance / 2d) * 2d * Wgs84EquatorialRadius;
+            var mapDistance = Math.Tan(distance / 2d) * 2d * Wgs84MeanRadius;
 
             return new Point(mapDistance * Math.Sin(azimuth), mapDistance * Math.Cos(azimuth));
         }
@@ -50,7 +50,7 @@ namespace MapControl
 
             var azimuth = Math.Atan2(x, y);
             var mapDistance = Math.Sqrt(x * x + y * y);
-            var distance = 2d * Math.Atan(mapDistance / (2d * Wgs84EquatorialRadius));
+            var distance = 2d * Math.Atan(mapDistance / (2d * Wgs84MeanRadius));
 
             return Center.GetLocation(azimuth, distance);
         }
diff --git a/MapControl/Shared/WorldMercatorProjection.cs b/MapControl/Shared/WorldMercatorProjection.cs
index 0b934c58..72abbbdf 100644
--- a/MapControl/Shared/WorldMercatorProjection.cs
+++ b/MapControl/Shared/WorldMercatorProjection.cs
@@ -13,6 +13,8 @@ namespace MapControl
     /// </summary>
     public class WorldMercatorProjection : MapProjection
     {
+        public static readonly double Wgs84Eccentricity = Math.Sqrt((2d - Wgs84Flattening) * Wgs84Flattening);
+
         public const string DefaultCrsId = "EPSG:3395";
 
         public WorldMercatorProjection()
diff --git a/MapProjections/Shared/WorldMercatorProjection.cs b/MapProjections/Shared/WorldMercatorProjection.cs
index 3019e4d9..874f69b0 100644
--- a/MapProjections/Shared/WorldMercatorProjection.cs
+++ b/MapProjections/Shared/WorldMercatorProjection.cs
@@ -43,7 +43,7 @@ namespace MapControl.Projections
         public override Point RelativeScale(double latitude, double longitude)
         {
             var lat = latitude * Math.PI / 180d;
-            var eSinLat = Wgs84Eccentricity * Math.Sin(lat);
+            var eSinLat = MapControl.WorldMercatorProjection.Wgs84Eccentricity * Math.Sin(lat);
             var k = Math.Sqrt(1d - eSinLat * eSinLat) / Math.Cos(lat); // p.44 (7-8)
 
             return new Point(k, k);