diff --git a/lib/origin/selectable.rb b/lib/origin/selectable.rb
index a7560ad..0022d9b 100644
--- a/lib/origin/selectable.rb
+++ b/lib/origin/selectable.rb
@@ -138,8 +138,6 @@ def exists(criterion = nil)
     # @note The only valid geometry shapes for a $geoIntersects are:
     #   :intersects_line, :intersects_point, and :intersects_polygon.
     #
-    # @note The only valid geometry shape for a $geoWithin is :within_polygon
-    #
     # @example Add a geo intersect criterion for a line.
     #   query.geo_spacial(:location.intersects_line => [[ 1, 10 ], [ 2, 10 ]])
     #
@@ -147,10 +145,16 @@ def exists(criterion = nil)
     #   query.geo_spacial(:location.intersects_point => [[ 1, 10 ]])
     #
     # @example Add a geo intersect criterion for a polygon.
-    #   query.geo_spacial(:location.intersects_polygon => [[ 1, 10 ], [ 2, 10 ], [ 1, 10 ]])
+    #   query.geo_spacial(:location.intersects_polygon => [[[ 1, 10 ], [ 2, 10 ], [ 1, 10 ]]])
     #
     # @example Add a geo within criterion for a polygon.
-    #   query.geo_spacial(:location.within_polygon => [[ 1, 10 ], [ 2, 10 ], [ 1, 10 ]])
+    #   query.geo_spacial(:location.within_polygon => [[[ 1, 10 ], [ 2, 10 ], [ 1, 10 ]]])
+    #
+    # @example Add a geo within criterian for a circle.
+    #   query.geo_spacial(:location.within_circle => [[x, y], radius])
+    #
+    # @example Add a geo within criterian for a sphere. Radius specified in radians.
+    #   query.geo_spacial(:location.within_sphere => [[x, y], radius])
     #
     # @param [ Hash ] criterion The criterion.
     #
@@ -172,6 +176,8 @@ def geo_spacial(criterion = nil)
     key :within_polygon, :override, "$geoWithin", "$geometry" do |value|
       { "type" => POLYGON, "coordinates" => value }
     end
+    key :within_circle, :override, "$geoWithin", "$center"
+    key :within_sphere, :override, "$geoWithin", "$centerSphere"
 
     # Add the $gt criterion to the selector.
     #
diff --git a/spec/origin/selectable_spec.rb b/spec/origin/selectable_spec.rb
index 6adc7ca..8059c1a 100644
--- a/spec/origin/selectable_spec.rb
+++ b/spec/origin/selectable_spec.rb
@@ -1075,6 +1075,46 @@ def localized?
 
         it_behaves_like "a cloning selection"
       end
+
+
+      context "when the geometry is a circle" do
+
+        let(:selection) do
+          query.geo_spacial(:location.within_circle => [[ 1, 10 ], 200])
+        end
+
+        it "adds the $center expression" do
+          expect(selection.selector).to eq({
+            "location" => {
+              "$geoWithin" => {
+                "$center" => [[1,10], 200]
+              }
+            }
+          })
+        end
+
+        it_behaves_like "a cloning selection"
+      end
+
+      context "when the geometry is a spherical circle" do
+
+        let(:selection) do
+          query.geo_spacial(:location.within_sphere => [[ 1, 10 ], 200])
+        end
+
+        it "adds the $center expression" do
+          expect(selection.selector).to eq({
+            "location" => {
+              "$geoWithin" => {
+                "$centerSphere" => [[1,10], 200]
+              }
+            }
+          })
+        end
+
+        it_behaves_like "a cloning selection"
+      end
+
     end
   end