diff --git a/MapProjections/Shared/AutoUtmProjection.cs b/MapProjections/Shared/AutoUtmProjection.cs
index 14c67142..8fd1d0a8 100644
--- a/MapProjections/Shared/AutoUtmProjection.cs
+++ b/MapProjections/Shared/AutoUtmProjection.cs
@@ -3,6 +3,7 @@
 // Licensed under the Microsoft Public License (Ms-PL)
 
 using ProjNet.CoordinateSystems;
+using System;
 using System.Windows;
 
 namespace MapControl.Projections
@@ -21,7 +22,7 @@ namespace MapControl.Projections
 
         public bool UseZoneCrsId { get; set; }
 
-        public override Point LocationToMap(Location location)
+        public override Point? LocationToMap(Location location)
         {
             UpdateZone();
 
@@ -39,7 +40,7 @@ namespace MapControl.Projections
         {
             var north = Center.Latitude >= 0d;
             var lon = Location.NormalizeLongitude(Center.Longitude);
-            var zone = (int)(lon + 180d) / 6 + 1;
+            var zone = (int)Math.Floor(lon / 6d) + 31;
 
             if (ZoneNumber != zone || ZoneIsNorth != north)
             {
diff --git a/MapProjections/Shared/GeoApiProjection.cs b/MapProjections/Shared/GeoApiProjection.cs
index 79de1a00..22996be3 100644
--- a/MapProjections/Shared/GeoApiProjection.cs
+++ b/MapProjections/Shared/GeoApiProjection.cs
@@ -116,7 +116,7 @@ namespace MapControl.Projections
 
         public IMathTransform MapToLocationTransform { get; private set; }
 
-        public override Point LocationToMap(Location location)
+        public override Point? LocationToMap(Location location)
         {
             if (LocationToMapTransform == null)
             {
@@ -126,6 +126,11 @@ namespace MapControl.Projections
             var coordinate = LocationToMapTransform.Transform(
                 new Coordinate(location.Longitude, location.Latitude));
 
+            if (coordinate == null)
+            {
+                return null;
+            }
+
             return new Point(coordinate.X * scaleFactor, coordinate.Y * scaleFactor);
         }
 
@@ -142,7 +147,7 @@ namespace MapControl.Projections
             return new Location(coordinate.Y, coordinate.X);
         }
 
-        public override string GetBboxValue(Rect rect)
+        public override string GetBboxValue(MapRect rect)
         {
             return string.Format(CultureInfo.InvariantCulture, bboxFormat,
                 rect.X / scaleFactor, rect.Y / scaleFactor,
diff --git a/MapProjections/Shared/PolarStereographicProjection.cs b/MapProjections/Shared/PolarStereographicProjection.cs
index 862a13ef..2aab6858 100644
--- a/MapProjections/Shared/PolarStereographicProjection.cs
+++ b/MapProjections/Shared/PolarStereographicProjection.cs
@@ -33,7 +33,7 @@ namespace MapControl.Projections
             FalseNorthing = falseNorthing;
         }
 
-        public override Vector GetRelativeScale(Location location)
+        public override Scale GetRelativeScale(Location location)
         {
             var lat = (IsNorth ? location.Latitude : -location.Latitude) * Math.PI / 180d;
             var a = Wgs84EquatorialRadius;
@@ -45,10 +45,10 @@ namespace MapControl.Projections
             var m = Math.Cos(lat) / Math.Sqrt(1d - eSinLat * eSinLat);
             var k = rho / (a * m);
 
-            return new Vector(k, k);
+            return new Scale(k, k);
         }
 
-        public override Point LocationToMap(Location location)
+        public override Point? LocationToMap(Location location)
         {
             var lat = location.Latitude * Math.PI / 180d;
             var lon = location.Longitude * Math.PI / 180d;
diff --git a/MapProjections/Shared/WebMercatorProjection.cs b/MapProjections/Shared/WebMercatorProjection.cs
index 1a0c48d1..b10bb785 100644
--- a/MapProjections/Shared/WebMercatorProjection.cs
+++ b/MapProjections/Shared/WebMercatorProjection.cs
@@ -21,11 +21,11 @@ namespace MapControl.Projections
             CoordinateSystem = ProjectedCoordinateSystem.WebMercator;
         }
 
-        public override Vector GetRelativeScale(Location location)
+        public override Scale GetRelativeScale(Location location)
         {
             var k = 1d / Math.Cos(location.Latitude * Math.PI / 180d); // p.44 (7-3)
 
-            return new Vector(k, k);
+            return new Scale(k, k);
         }
     }
 }
diff --git a/MapProjections/Shared/WorldMercatorProjection.cs b/MapProjections/Shared/WorldMercatorProjection.cs
index bb3adc7b..3a6a158e 100644
--- a/MapProjections/Shared/WorldMercatorProjection.cs
+++ b/MapProjections/Shared/WorldMercatorProjection.cs
@@ -42,13 +42,13 @@ namespace MapControl.Projections
                 + "AUTHORITY[\"EPSG\",\"3395\"]]";
         }
 
-        public override Vector GetRelativeScale(Location location)
+        public override Scale GetRelativeScale(Location location)
         {
             var lat = location.Latitude * Math.PI / 180d;
             var eSinLat = Wgs84Eccentricity * Math.Sin(lat);
             var k = Math.Sqrt(1d - eSinLat * eSinLat) / Math.Cos(lat); // p.44 (7-8)
 
-            return new Vector(k, k);
+            return new Scale(k, k);
         }
     }
 }