diff --git a/simgear/canvas/elements/CanvasMap.cxx b/simgear/canvas/elements/CanvasMap.cxx
index cca235b4..e15dc13b 100644
--- a/simgear/canvas/elements/CanvasMap.cxx
+++ b/simgear/canvas/elements/CanvasMap.cxx
@@ -47,6 +47,12 @@ namespace canvas
   const std::string GEO = "-geo";
   const std::string HDG = "hdg";
   const std::string Map::TYPE_NAME = "map";
+  const std::string WEB_MERCATOR = "webmercator";
+  const std::string REF_LAT = "ref-lat";
+  const std::string REF_LON = "ref-lon";
+  const std::string SCREEN_RANGE = "screen-range";
+  const std::string RANGE = "range";
+  const std::string PROJECTION = "projection";
 
   //----------------------------------------------------------------------------
   void Map::staticInit()
@@ -64,12 +70,16 @@ namespace canvas
             const SGPropertyNode_ptr& node,
             const Style& parent_style,
             ElementWeakPtr parent ):
-    Group(canvas, node, parent_style, parent),
-    // TODO make projection configurable
-    _projection(new SansonFlamsteedProjection),
-    _projection_dirty(true)
+    Group(canvas, node, parent_style, parent)
   {
     staticInit();
+    if (node->getChild(PROJECTION) &&
+        (node->getChild(PROJECTION)->getStringValue() == WEB_MERCATOR)) {
+      _projection = (boost::shared_ptr<HorizontalProjection>) new WebMercatorProjection();
+    } else {
+      _projection = (boost::shared_ptr<HorizontalProjection>) new SansonFlamsteedProjection();
+    }
+    _projection_dirty = true;
   }
 
   //----------------------------------------------------------------------------
@@ -162,10 +172,10 @@ namespace canvas
     if( child->getParent() != _node )
       return Group::childChanged(child);
 
-    if(    child->getNameString() == "ref-lat"
-        || child->getNameString() == "ref-lon" )
-      _projection->setWorldPosition( _node->getDoubleValue("ref-lat"),
-                                     _node->getDoubleValue("ref-lon") );
+    if(    child->getNameString() == REF_LAT
+        || child->getNameString() == REF_LON )
+      _projection->setWorldPosition( _node->getDoubleValue(REF_LAT),
+                                     _node->getDoubleValue(REF_LON) );
     else if( child->getNameString() == HDG )
     {
       _projection->setOrientation(child->getFloatValue());
@@ -174,11 +184,23 @@ namespace canvas
                            ++it )
         hdgNodeChanged(*it);
     }
-    else if( child->getNameString() == "range" )
+    else if( child->getNameString() == RANGE )
       _projection->setRange(child->getDoubleValue());
-    else if( child->getNameString() == "screen-range" )
+    else if( child->getNameString() == SCREEN_RANGE )
       _projection->setScreenRange(child->getDoubleValue());
-    else
+    else if( child->getNameString() == PROJECTION ) {
+      if (child->getStringValue() == WEB_MERCATOR) {
+        _projection = (boost::shared_ptr<HorizontalProjection>) new WebMercatorProjection();
+      } else {
+        _projection = (boost::shared_ptr<HorizontalProjection>) new SansonFlamsteedProjection();
+      }
+      _projection->setWorldPosition(_node->getDoubleValue(REF_LAT),
+                                    _node->getDoubleValue(REF_LON) );
+      _projection->setOrientation(_node->getFloatValue(HDG));
+      _projection->setScreenRange(_node->getDoubleValue(SCREEN_RANGE));
+      _projection->setRange(_node->getDoubleValue(RANGE));
+      _projection_dirty = true;
+    } else
       return Group::childChanged(child);
 
     _projection_dirty = true;
diff --git a/simgear/canvas/elements/map/projection.hxx b/simgear/canvas/elements/map/projection.hxx
index d60f7d5f..e58b9f94 100644
--- a/simgear/canvas/elements/map/projection.hxx
+++ b/simgear/canvas/elements/map/projection.hxx
@@ -190,6 +190,32 @@ namespace canvas
       }
   };
 
+  /**
+   * WebMercator projection, relative to the projection center.
+   * Required for Slippy Maps - i.e. openstreetmap
+   */
+  class WebMercatorProjection:
+    public HorizontalProjection
+  {
+    protected:
+
+      virtual ScreenPosition project(double lat, double lon) const
+      {
+        double d_lat = lat - _ref_lat,
+               d_lon = lon - _ref_lon;
+        double r = 6378137.f / 1852; // Equatorial radius divided by ?
+
+        ScreenPosition pos;
+
+        pos.x = r * d_lon;
+        pos.y = r * (log(tan(d_lat) + 1.0 / cos(d_lat)));
+        //pos.x = lon;
+        //pos.y = log(tan(lat) + 1.0 / cos(lat));
+        return pos;
+      }
+  };
+
+
 } // namespace canvas
 } // namespace simgear
 
diff --git a/simgear/nasal/mathlib.c b/simgear/nasal/mathlib.c
index 564168c5..7c8210f0 100644
--- a/simgear/nasal/mathlib.c
+++ b/simgear/nasal/mathlib.c
@@ -109,7 +109,7 @@ static naRef f_fmod(naContext c, naRef me, int argc, naRef* args)
     naRef b = naNumValue(argc > 1 ? args[1] : naNil());
     if(naIsNil(a) || naIsNil(b))
         naRuntimeError(c, "non numeric arguments to fmod()");
-    
+
     a.num = fmod(a.num, b.num);
     return VALIDATE(a);
 }
@@ -119,7 +119,7 @@ static naRef f_clamp(naContext c, naRef me, int argc, naRef* args)
     naRef a = naNumValue(argc > 0 ? args[0] : naNil());
     naRef min = naNumValue(argc > 1 ? args[1] : naNil());
     naRef max = naNumValue(argc > 2 ? args[2] : naNil());
-    
+
     if(naIsNil(a) || naIsNil(min) || naIsNil(max))
         naRuntimeError(c, "non numeric arguments to clamp()");
 
@@ -133,10 +133,10 @@ static naRef f_periodic(naContext c, naRef me, int argc, naRef* args)
     naRef a = naNumValue(argc > 0 ? args[0] : naNil());
     naRef b = naNumValue(argc > 1 ? args[1] : naNil());
     naRef x = naNumValue(argc > 2 ? args[2] : naNil());
-    
+
     if(naIsNil(a) || naIsNil(b) || naIsNil(x))
         naRuntimeError(c, "non numeric arguments to periodic()");
-  
+
     range = b.num - a.num;
     x.num = x.num - range*floor((x.num - a.num)/range);
     // two security checks that can only happen due to roundoff
@@ -145,7 +145,7 @@ static naRef f_periodic(naContext c, naRef me, int argc, naRef* args)
     if (b.num <= x.num)
         x.num = b.num;
     return VALIDATE(x);
-      
+
 //    x.num = SGMiscd::normalizePeriodic(a, b, x);
     return VALIDATE(x);
 }
@@ -156,7 +156,7 @@ static naRef f_round(naContext c, naRef me, int argc, naRef* args)
     naRef b = naNumValue(argc > 1 ? args[1] : naNil());
 #ifdef _MSC_VER
     double x,y;
-#endif    
+#endif
     if(naIsNil(a))
         naRuntimeError(c, "non numeric arguments to round()");
     if (naIsNil(b))
@@ -169,21 +169,31 @@ static naRef f_round(naContext c, naRef me, int argc, naRef* args)
     double x = round(a.num / b.num);
 #endif
     a.num = x * b.num;
-    
+
     return VALIDATE(a);
 }
 
 
 static naRef f_tan(naContext c, naRef me, int argc, naRef* args)
 {
-    naRef a = naNumValue(argc > 0 ? args[0] : naNil());    
+    naRef a = naNumValue(argc > 0 ? args[0] : naNil());
     if(naIsNil(a))
         naRuntimeError(c, "non numeric arguments to tan()");
-    
+
    a.num = tan(a.num);
    return VALIDATE(a);
 }
 
+static naRef f_atan(naContext c, naRef me, int argc, naRef* args)
+{
+    naRef a = naNumValue(argc > 0 ? args[0] : naNil());
+    if(naIsNil(a))
+        naRuntimeError(c, "non numeric arguments to tan()");
+
+   a.num = atan(a.num);
+   return VALIDATE(a);
+}
+
 static naRef f_asin(naContext c, naRef me, int argc, naRef* args)
 {
     naRef a = naNumValue(argc > 0 ? args[0] : naNil());
@@ -210,15 +220,16 @@ static naCFuncItem funcs[] = {
     { "pow", f_pow },
     { "sqrt", f_sqrt },
     { "atan2", f_atan2 },
+    { "atan", f_atan },
     { "floor", f_floor },
     { "ceil", f_ceil },
     { "fmod", f_fmod },
     { "clamp", f_clamp },
-    { "periodic", f_periodic },    
-    { "round", f_round }, 
-    { "tan", f_tan },   
+    { "periodic", f_periodic },
+    { "round", f_round },
+    { "tan", f_tan },
     { "acos", f_acos },
-    { "asin", f_asin },   
+    { "asin", f_asin },
     { 0 }
 };