diff --git a/.travis.yml b/.travis.yml
index 967786acd..5de9299f0 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -45,6 +45,12 @@ matrix:
       env: JOBS=4 MASON_PUBLISH=true _CXX="ccache clang++ -Qunused-arguments"
 
 before_install:
+ # workaround travis rvm bug
+ # http://superuser.com/questions/1044130/why-am-i-having-how-can-i-fix-this-error-shell-session-update-command-not-f
+ - |
+   if [[ "${TRAVIS_OS_NAME}" == "osx" ]]; then
+     rvm get head || true
+   fi
  - if [[ ${_CXX:-false} != false ]]; then export CXX=${_CXX}; fi
  - if [[ ${_CC:-false} != false ]]; then export CC=${_CC}; fi
  - source scripts/travis-common.sh
diff --git a/deps/mapbox/variant b/deps/mapbox/variant
index b5728ad76..388376ac9 160000
--- a/deps/mapbox/variant
+++ b/deps/mapbox/variant
@@ -1 +1 @@
-Subproject commit b5728ad76e1402c130a9330aa44b6f4b655b13b4
+Subproject commit 388376ac9f0102feba2d2122873b08e15a66a879
diff --git a/include/mapnik/config.hpp b/include/mapnik/config.hpp
index 5b4c82be1..a05caf9d4 100644
--- a/include/mapnik/config.hpp
+++ b/include/mapnik/config.hpp
@@ -52,10 +52,18 @@
 
 #define PROJ_ENVELOPE_POINTS 20
 
-#ifndef BOOST_MPL_LIMIT_VECTOR_SIZE
 #define BOOST_MPL_CFG_NO_PREPROCESSED_HEADERS
-#define BOOST_MPL_LIMIT_VECTOR_SIZE 30
+
+#ifndef BOOST_MPL_LIMIT_VECTOR_SIZE
+ #define BOOST_MPL_LIMIT_VECTOR_SIZE 30
 #else
-#warning "WARNING: BOOST_MPL_LIMIT_VECTOR_SIZE is already defined. Ensure config.hpp is included before any Boost headers"
+ #warning "WARNING: BOOST_MPL_LIMIT_VECTOR_SIZE is already defined. Ensure config.hpp is included before any Boost headers"
 #endif
+
+#ifndef BOOST_MPL_LIMIT_LIST_SIZE
+ #define BOOST_MPL_LIMIT_LIST_SIZE 30
+#else
+ #warning "WARNING: BOOST_MPL_LIMIT_LIST_SIZE is already defined. Ensure config.hpp is included before any Boost headers"
+#endif
+
 #endif // MAPNIK_CONFIG_HPP
diff --git a/include/mapnik/feature.hpp b/include/mapnik/feature.hpp
index f340c83d6..1300d3220 100644
--- a/include/mapnik/feature.hpp
+++ b/include/mapnik/feature.hpp
@@ -154,7 +154,7 @@ public:
 
     inline bool has_key(context_type::key_type const& key) const
     {
-        return (ctx_->mapping_.find(key) != ctx_->mapping_.end());
+        return (ctx_->mapping_.count(key) == 1);
     }
 
     inline value_type const& get(context_type::key_type const& key) const
diff --git a/include/mapnik/featureset.hpp b/include/mapnik/featureset.hpp
index c6829d1eb..6886d8755 100644
--- a/include/mapnik/featureset.hpp
+++ b/include/mapnik/featureset.hpp
@@ -41,8 +41,23 @@ struct MAPNIK_DECL Featureset : private util::noncopyable
     virtual ~Featureset() {}
 };
 
+
+struct MAPNIK_DECL empty_featureset final : Featureset
+{
+    feature_ptr next()
+    {
+        return feature_ptr();
+    }
+    ~empty_featureset() {}
+};
+
 using featureset_ptr = std::shared_ptr<Featureset>;
 
+inline featureset_ptr make_empty_featureset()
+{
+    return std::make_shared<empty_featureset>();
+}
+
 }
 
 #endif // MAPNIK_FEATURESET_HPP
diff --git a/include/mapnik/geometry.hpp b/include/mapnik/geometry.hpp
index f97e9e6c6..c298fa61d 100644
--- a/include/mapnik/geometry.hpp
+++ b/include/mapnik/geometry.hpp
@@ -148,11 +148,7 @@ struct geometry : geometry_base<T>
 
     geometry()
         : geometry_base<T>() {} // empty
-
-    template <typename G>
-    geometry(G && geom)
-        : geometry_base<T>(std::forward<G>(geom)) {}
-
+    using geometry_base<T>::geometry_base;
 };
 
 template <typename T>
diff --git a/include/mapnik/json/extract_bounding_box_grammar_impl.hpp b/include/mapnik/json/extract_bounding_box_grammar_impl.hpp
index 9e21baa08..25ddbcd92 100644
--- a/include/mapnik/json/extract_bounding_box_grammar_impl.hpp
+++ b/include/mapnik/json/extract_bounding_box_grammar_impl.hpp
@@ -110,7 +110,7 @@ extract_bounding_box_grammar<Iterator, Boxes, ErrorHandler>::extract_bounding_bo
                                                >> *((json.key_value - lit("\"features\"")) >> lit(','))
                                                >> lit("\"features\"")
                                                >> lit(':'))
-                                          >> lit('[') >> (feature(_r1,_a) % lit(',')) >> lit(']')
+                                          >> lit('[') >> -(feature(_r1,_a) % lit(',')) >> lit(']')
         ;
 
     feature = raw[lit('{')[_a = 1]
diff --git a/include/mapnik/palette.hpp b/include/mapnik/palette.hpp
index 5f9627239..1276d1302 100644
--- a/include/mapnik/palette.hpp
+++ b/include/mapnik/palette.hpp
@@ -43,6 +43,7 @@ using rgba_hash_table = std::unordered_map<unsigned int, unsigned char>;
 
 // stl
 #include <vector>
+#include <tuple>
 
 #define U2RED(x) ((x)&0xff)
 #define U2GREEN(x) (((x)>>8)&0xff)
@@ -53,7 +54,8 @@ namespace mapnik {
 
 struct rgba;
 
-struct MAPNIK_DECL rgb {
+struct MAPNIK_DECL rgb
+{
     std::uint8_t r;
     std::uint8_t g;
     std::uint8_t b;
@@ -92,7 +94,7 @@ struct MAPNIK_DECL rgba
           b(U2BLUE(c)),
           a(U2ALPHA(c)) {}
 
-    inline bool operator==(const rgba& y) const
+    inline bool operator==(rgba const& y) const
     {
         return r == y.r && g == y.g && b == y.b && a == y.a;
     }
@@ -103,18 +105,27 @@ struct MAPNIK_DECL rgba
         bool operator() (const rgba& x, const rgba& y) const;
     };
 
+    inline bool operator<(rgba const& y) const
+    {
+        return std::tie(r, g, b, a) < std::tie(y.r, y.g, y.b, y.a);
+    }
+
 };
 
 
-class MAPNIK_DECL rgba_palette : private util::noncopyable {
+class MAPNIK_DECL rgba_palette : private util::noncopyable
+{
 public:
     enum palette_type { PALETTE_RGBA = 0, PALETTE_RGB = 1, PALETTE_ACT = 2 };
 
     explicit rgba_palette(std::string const& pal, palette_type type = PALETTE_RGBA);
     rgba_palette();
 
-    const std::vector<rgb>& palette() const;
-    const std::vector<unsigned>& alphaTable() const;
+    inline std::vector<rgb> const& palette() const { return rgb_pal_;}
+    inline std::vector<unsigned> const& alpha_table() const { return alpha_pal_;}
+
+    inline std::vector<rgb>& palette() { return rgb_pal_;}
+    inline std::vector<unsigned>& alpha_table() { return alpha_pal_;}
 
     unsigned char quantize(unsigned c) const;
 
diff --git a/include/mapnik/params.hpp b/include/mapnik/params.hpp
index a38fa54e7..535cacb38 100644
--- a/include/mapnik/params.hpp
+++ b/include/mapnik/params.hpp
@@ -51,6 +51,10 @@ struct value_holder : value_holder_base
     value_holder()
         : value_holder_base() {}
 
+    // C-string -> std::string
+    value_holder(char const* str)
+        : value_holder(std::string(str)) {}
+
     // perfect forwarding
     template <typename T>
     value_holder(T && obj)
diff --git a/include/mapnik/png_io.hpp b/include/mapnik/png_io.hpp
index 051ea6b4e..9f8b38d8f 100644
--- a/include/mapnik/png_io.hpp
+++ b/include/mapnik/png_io.hpp
@@ -39,7 +39,7 @@ extern "C"
 {
 #include <png.h>
 }
-
+#include <set>
 #pragma GCC diagnostic pop
 
 #define MAX_OCTREE_LEVELS 4
@@ -515,19 +515,19 @@ void save_as_png8_oct(T1 & file,
     }
 
     //transparency values per palette index
-    std::vector<unsigned> alphaTable;
-    //alphaTable.resize(palette.size());//allow semitransparency also in almost opaque range
+    std::vector<unsigned> alpha_table;
+    //alpha_table.resize(palette.size());//allow semitransparency also in almost opaque range
     if (opts.trans_mode != 0)
     {
-        alphaTable.resize(palette.size() - cols[TRANSPARENCY_LEVELS-1]);
+        alpha_table.resize(palette.size() - cols[TRANSPARENCY_LEVELS-1]);
     }
 
     if (palette.size() > 16 )
     {
         // >16 && <=256 colors -> write 8-bit color depth
         image_gray8 reduced_image(width,height);
-        reduce_8(image, reduced_image, trees, limits, TRANSPARENCY_LEVELS, alphaTable);
-        save_as_png(file,palette,reduced_image,width,height,8,alphaTable,opts);
+        reduce_8(image, reduced_image, trees, limits, TRANSPARENCY_LEVELS, alpha_table);
+        save_as_png(file,palette,reduced_image,width,height,8,alpha_table,opts);
     }
     else if (palette.size() == 1)
     {
@@ -535,13 +535,13 @@ void save_as_png8_oct(T1 & file,
         unsigned image_width  = ((width + 15) >> 3) & ~1U; // 1-bit image, round up to 16-bit boundary
         unsigned image_height = height;
         image_gray8 reduced_image(image_width,image_height);
-        reduce_1(image,reduced_image,trees, limits, alphaTable);
+        reduce_1(image,reduced_image,trees, limits, alpha_table);
         if (meanAlpha<255 && cols[0]==0)
         {
-            alphaTable.resize(1);
-            alphaTable[0] = meanAlpha;
+            alpha_table.resize(1);
+            alpha_table[0] = meanAlpha;
         }
-        save_as_png(file,palette,reduced_image,width,height,1,alphaTable,opts);
+        save_as_png(file,palette,reduced_image,width,height,1,alpha_table,opts);
     }
     else
     {
@@ -549,8 +549,8 @@ void save_as_png8_oct(T1 & file,
         unsigned image_width  = ((width + 7) >> 1) & ~3U; // 4-bit image, round up to 32-bit boundary
         unsigned image_height = height;
         image_gray8 reduced_image(image_width,image_height);
-        reduce_4(image, reduced_image, trees, limits, TRANSPARENCY_LEVELS, alphaTable);
-        save_as_png(file,palette,reduced_image,width,height,4,alphaTable,opts);
+        reduce_4(image, reduced_image, trees, limits, TRANSPARENCY_LEVELS, alpha_table);
+        save_as_png(file,palette,reduced_image,width,height,4,alpha_table,opts);
     }
 }
 
@@ -560,7 +560,7 @@ void save_as_png8(T1 & file,
                   T2 const& image,
                   T3 const & tree,
                   std::vector<mapnik::rgb> const& palette,
-                  std::vector<unsigned> const& alphaTable,
+                  std::vector<unsigned> const& alpha_table,
                   png_options const& opts)
 {
     unsigned width = image.width();
@@ -579,7 +579,7 @@ void save_as_png8(T1 & file,
                 row_out[x] = tree.quantize(row[x]);
             }
         }
-        save_as_png(file, palette, reduced_image, width, height, 8, alphaTable, opts);
+        save_as_png(file, palette, reduced_image, width, height, 8, alpha_table, opts);
     }
     else if (palette.size() == 1)
     {
@@ -588,7 +588,7 @@ void save_as_png8(T1 & file,
         unsigned image_height = height;
         image_gray8 reduced_image(image_width, image_height);
         reduced_image.set(0);
-        save_as_png(file, palette, reduced_image, width, height, 1, alphaTable, opts);
+        save_as_png(file, palette, reduced_image, width, height, 1, alpha_table, opts);
     }
     else
     {
@@ -612,7 +612,7 @@ void save_as_png8(T1 & file,
                 row_out[x>>1] |= index;
             }
         }
-        save_as_png(file, palette, reduced_image, width, height, 4, alphaTable, opts);
+        save_as_png(file, palette, reduced_image, width, height, 4, alpha_table, opts);
     }
 }
 
@@ -623,6 +623,7 @@ void save_as_png8_hex(T1 & file,
 {
     unsigned width = image.width();
     unsigned height = image.height();
+
     if (width + height > 3) // at least 3 pixels (hextree implementation requirement)
     {
         // structure for color quantization
@@ -647,20 +648,44 @@ void save_as_png8_hex(T1 & file,
         }
 
         //transparency values per palette index
-        std::vector<mapnik::rgba> pal;
-        tree.create_palette(pal);
+        std::vector<mapnik::rgba> rgba_palette;
+        tree.create_palette(rgba_palette);
+        auto size = rgba_palette.size();
         std::vector<mapnik::rgb> palette;
-        std::vector<unsigned> alphaTable;
-        for (unsigned i=0; i<pal.size(); ++i)
+        std::vector<unsigned> alpha_table;
+        palette.reserve(size);
+        alpha_table.reserve(size);
+        for (auto const& c : rgba_palette)
         {
-            palette.push_back(rgb(pal[i].r, pal[i].g, pal[i].b));
-            alphaTable.push_back(pal[i].a);
+            palette.emplace_back(c.r, c.g, c.b);
+            alpha_table.push_back(c.a);
         }
-        save_as_png8<T1, T2, hextree<mapnik::rgba> >(file, image, tree, palette, alphaTable, opts);
+        save_as_png8<T1, T2, hextree<mapnik::rgba> >(file, image, tree, palette, alpha_table, opts);
     }
     else
     {
-        throw std::runtime_error("Can't quantize images with less than 3 pixels");
+
+        std::set<mapnik::rgba> colors;
+        for (unsigned y = 0; y < height; ++y)
+        {
+            typename T2::pixel_type const * row = image.get_row(y);
+
+            for (unsigned x = 0; x < width; ++x)
+            {
+                unsigned val = row[x];
+                colors.emplace(U2RED(val), U2GREEN(val), U2BLUE(val), U2ALPHA(val));
+            }
+        }
+        std::string str;
+        for (auto c : colors)
+        {
+            str.push_back(c.r);
+            str.push_back(c.g);
+            str.push_back(c.b);
+            str.push_back(c.a);
+        }
+        rgba_palette pal(str, rgba_palette::PALETTE_RGBA);
+        save_as_png8<T1, T2, rgba_palette>(file, image, pal, pal.palette(), pal.alpha_table(), opts);
     }
 }
 
@@ -670,7 +695,7 @@ void save_as_png8_pal(T1 & file,
                       rgba_palette const& pal,
                       png_options const& opts)
 {
-    save_as_png8<T1, T2, rgba_palette>(file, image, pal, pal.palette(), pal.alphaTable(), opts);
+    save_as_png8<T1, T2, rgba_palette>(file, image, pal, pal.palette(), pal.alpha_table(), opts);
 }
 
 }
diff --git a/include/mapnik/symbolizer_base.hpp b/include/mapnik/symbolizer_base.hpp
index fc88c579c..f07cf3d2a 100644
--- a/include/mapnik/symbolizer_base.hpp
+++ b/include/mapnik/symbolizer_base.hpp
@@ -101,7 +101,7 @@ struct strict_value : value_base_type
     strict_value() = default;
 
     strict_value(const char* val)
-        : value_base_type(val) {}
+        : value_base_type(std::string(val)) {}
 
     template <typename T>
     strict_value(T const& obj)
diff --git a/include/mapnik/util/variant.hpp b/include/mapnik/util/variant.hpp
index 3fb00b388..87cfb70ff 100644
--- a/include/mapnik/util/variant.hpp
+++ b/include/mapnik/util/variant.hpp
@@ -51,13 +51,13 @@ public:
 // unary visitor interface
 // const
 template <typename F, typename V>
-auto VARIANT_INLINE static apply_visitor(F && f, V const& v) -> decltype(V::visit(v, f))
+auto VARIANT_INLINE static apply_visitor(F && f, V const& v) -> decltype(V::visit(v, std::forward<F>(f)))
 {
     return V::visit(v, std::forward<F>(f));
 }
 // non-const
 template <typename F, typename V>
-auto VARIANT_INLINE static apply_visitor(F && f, V & v) -> decltype(V::visit(v, f))
+auto VARIANT_INLINE static apply_visitor(F && f, V & v) -> decltype(V::visit(v, std::forward<F>(f)))
 {
     return V::visit(v, std::forward<F>(f));
 }
@@ -65,14 +65,14 @@ auto VARIANT_INLINE static apply_visitor(F && f, V & v) -> decltype(V::visit(v,
 // binary visitor interface
 // const
 template <typename F, typename V>
-auto VARIANT_INLINE static apply_visitor(F && f, V const& v0, V const& v1) -> decltype(V::binary_visit(v0, v1, f))
+auto VARIANT_INLINE static apply_visitor(F && f, V const& v0, V const& v1) -> decltype(V::binary_visit(v0, v1, std::forward<F>(f)))
 {
     return V::binary_visit(v0, v1, std::forward<F>(f));
 }
 
 // non-const
 template <typename F, typename V>
-auto VARIANT_INLINE static apply_visitor(F && f, V & v0, V & v1) -> decltype(V::binary_visit(v0, v1, f))
+auto VARIANT_INLINE static apply_visitor(F && f, V & v0, V & v1) -> decltype(V::binary_visit(v0, v1, std::forward<F>(f)))
 {
     return V::binary_visit(v0, v1, std::forward<F>(f));
 }
diff --git a/include/mapnik/xml_attribute_cast.hpp b/include/mapnik/xml_attribute_cast.hpp
index fb3b7ebdc..cafa7e79a 100644
--- a/include/mapnik/xml_attribute_cast.hpp
+++ b/include/mapnik/xml_attribute_cast.hpp
@@ -55,7 +55,7 @@ struct do_xml_attribute_cast
 {
     static inline boost::optional<T> xml_attribute_cast_impl(xml_tree const& /*tree*/, std::string const& /*source*/)
     {
-        std::string err_msg("No conversion from std::string to");
+        std::string err_msg("No conversion from std::string to ");
         err_msg += std::string(typeid(T).name());
         throw std::runtime_error(err_msg);
     }
@@ -74,6 +74,19 @@ struct do_xml_attribute_cast<mapnik::boolean_type>
     }
 };
 
+// specialization for mapnik::value_bool
+template <>
+struct do_xml_attribute_cast<mapnik::value_bool>
+{
+    static inline boost::optional<mapnik::value_bool> xml_attribute_cast_impl(xml_tree const& /*tree*/, std::string const& source)
+    {
+        bool result;
+        if (mapnik::util::string2bool(source, result))
+            return boost::optional<mapnik::value_bool>(result);
+        return boost::optional<mapnik::value_bool>();
+    }
+};
+
 // specialization for int
 template <>
 struct do_xml_attribute_cast<int>
diff --git a/plugins/input/csv/csv_datasource.cpp b/plugins/input/csv/csv_datasource.cpp
index 6c1ff1014..4a246b404 100644
--- a/plugins/input/csv/csv_datasource.cpp
+++ b/plugins/input/csv/csv_datasource.cpp
@@ -431,7 +431,7 @@ mapnik::featureset_ptr csv_datasource::features(mapnik::query const& q) const
             return std::make_shared<csv_index_featureset>(filename_, filter, locator_, separator_, quote_, headers_, ctx_);
         }
     }
-    return mapnik::featureset_ptr();
+    return mapnik::make_empty_featureset();
 }
 
 mapnik::featureset_ptr csv_datasource::features_at_point(mapnik::coord2d const& pt, double tol) const
diff --git a/plugins/input/geojson/geojson_datasource.cpp b/plugins/input/geojson/geojson_datasource.cpp
index e9456f8e1..d2ebc2d54 100644
--- a/plugins/input/geojson/geojson_datasource.cpp
+++ b/plugins/input/geojson/geojson_datasource.cpp
@@ -587,8 +587,8 @@ mapnik::featureset_ptr geojson_datasource::features(mapnik::query const& q) cons
         }
 
     }
-    // otherwise return an empty featureset pointer
-    return mapnik::featureset_ptr();
+    // otherwise return an empty featureset
+    return mapnik::make_empty_featureset();
 }
 
 mapnik::featureset_ptr geojson_datasource::features_at_point(mapnik::coord2d const& pt, double tol) const
diff --git a/plugins/input/ogr/ogr_datasource.cpp b/plugins/input/ogr/ogr_datasource.cpp
index dc0fc9bec..2943962fc 100644
--- a/plugins/input/ogr/ogr_datasource.cpp
+++ b/plugins/input/ogr/ogr_datasource.cpp
@@ -560,7 +560,7 @@ featureset_ptr ogr_datasource::features(query const& q) const
         }
     }
 
-    return featureset_ptr();
+    return mapnik::make_empty_featureset();
 }
 
 featureset_ptr ogr_datasource::features_at_point(coord2d const& pt, double tol) const
@@ -603,5 +603,5 @@ featureset_ptr ogr_datasource::features_at_point(coord2d const& pt, double tol)
         }
     }
 
-    return featureset_ptr();
+    return mapnik::make_empty_featureset();
 }
diff --git a/plugins/input/pgraster/pgraster_datasource.cpp b/plugins/input/pgraster/pgraster_datasource.cpp
index 9390f3ace..ced1810b5 100644
--- a/plugins/input/pgraster/pgraster_datasource.cpp
+++ b/plugins/input/pgraster/pgraster_datasource.cpp
@@ -998,7 +998,7 @@ featureset_ptr pgraster_datasource::features_with_context(query const& q,process
 
     }
 
-    return featureset_ptr();
+    return mapnik::make_empty_featureset();
 }
 
 
@@ -1011,7 +1011,7 @@ featureset_ptr pgraster_datasource::features_at_point(coord2d const& pt, double
     if (pool)
     {
         shared_ptr<Connection> conn = pool->borrowObject();
-        if (!conn) return featureset_ptr();
+        if (!conn) return mapnik::make_empty_featureset();
 
         if (conn->isOK())
         {
@@ -1082,7 +1082,7 @@ featureset_ptr pgraster_datasource::features_at_point(coord2d const& pt, double
         }
     }
 
-    return featureset_ptr();
+    return mapnik::make_empty_featureset();
 }
 
 box2d<double> pgraster_datasource::envelope() const
diff --git a/plugins/input/postgis/postgis_datasource.cpp b/plugins/input/postgis/postgis_datasource.cpp
index 909cd58ba..2653e5757 100644
--- a/plugins/input/postgis/postgis_datasource.cpp
+++ b/plugins/input/postgis/postgis_datasource.cpp
@@ -479,7 +479,7 @@ postgis_datasource::postgis_datasource(parameters const& params)
         // Finally, add unique metadata to layer descriptor
         mapnik::parameters & extra_params = desc_.get_extra_parameters();
         // explicitly make copies of values due to https://github.com/mapnik/mapnik/issues/2651
-        extra_params["srid"] = srid_;
+        extra_params["srid"] = mapnik::value_integer(srid_);
         if (!key_field_.empty())
         {
             extra_params["key_field"] = key_field_;
@@ -942,7 +942,7 @@ featureset_ptr postgis_datasource::features_with_context(query const& q,processo
 
     }
 
-    return featureset_ptr();
+    return mapnik::make_empty_featureset();
 }
 
 
@@ -955,7 +955,7 @@ featureset_ptr postgis_datasource::features_at_point(coord2d const& pt, double t
     if (pool)
     {
         shared_ptr<Connection> conn = pool->borrowObject();
-        if (!conn) return featureset_ptr();
+        if (!conn) return mapnik::make_empty_featureset();
 
         if (conn->isOK())
         {
@@ -1030,7 +1030,7 @@ featureset_ptr postgis_datasource::features_at_point(coord2d const& pt, double t
         }
     }
 
-    return featureset_ptr();
+    return mapnik::make_empty_featureset();
 }
 
 box2d<double> postgis_datasource::envelope() const
diff --git a/plugins/input/raster/raster_datasource.cpp b/plugins/input/raster/raster_datasource.cpp
index 4d8b5f99a..38a6aa94c 100644
--- a/plugins/input/raster/raster_datasource.cpp
+++ b/plugins/input/raster/raster_datasource.cpp
@@ -224,5 +224,5 @@ featureset_ptr raster_datasource::features_at_point(coord2d const&, double tol)
 {
     MAPNIK_LOG_WARN(raster) << "raster_datasource: feature_at_point not supported";
 
-    return featureset_ptr();
+    return mapnik::make_empty_featureset();
 }
diff --git a/plugins/input/sqlite/sqlite_datasource.cpp b/plugins/input/sqlite/sqlite_datasource.cpp
index 939d9d319..37e44117b 100644
--- a/plugins/input/sqlite/sqlite_datasource.cpp
+++ b/plugins/input/sqlite/sqlite_datasource.cpp
@@ -551,7 +551,7 @@ featureset_ptr sqlite_datasource::features(query const& q) const
                                                      using_subquery_);
     }
 
-    return featureset_ptr();
+    return mapnik::make_empty_featureset();
 }
 
 featureset_ptr sqlite_datasource::features_at_point(coord2d const& pt, double tol) const
@@ -631,5 +631,5 @@ featureset_ptr sqlite_datasource::features_at_point(coord2d const& pt, double to
                                                      using_subquery_);
     }
 
-    return featureset_ptr();
+    return mapnik::make_empty_featureset();
 }
diff --git a/plugins/input/topojson/topojson_datasource.cpp b/plugins/input/topojson/topojson_datasource.cpp
index 502868562..e6cab26d8 100644
--- a/plugins/input/topojson/topojson_datasource.cpp
+++ b/plugins/input/topojson/topojson_datasource.cpp
@@ -284,7 +284,7 @@ mapnik::featureset_ptr topojson_datasource::features(mapnik::query const& q) con
         }
     }
     // otherwise return an empty featureset pointer
-    return mapnik::featureset_ptr();
+    return mapnik::make_empty_featureset();
 }
 
 mapnik::featureset_ptr topojson_datasource::features_at_point(mapnik::coord2d const& pt, double tol) const
diff --git a/src/datasource_cache.cpp b/src/datasource_cache.cpp
index 043b01093..3759a6ceb 100644
--- a/src/datasource_cache.cpp
+++ b/src/datasource_cache.cpp
@@ -117,7 +117,7 @@ datasource_ptr datasource_cache::create(parameters const& params)
 #endif
         create_ds create_datasource = reinterpret_cast<create_ds>(itr->second->get_symbol("create"));
 
-    if (! create_datasource)
+    if (!create_datasource)
     {
         throw std::runtime_error(std::string("Cannot load symbols: ") +
                                  itr->second->get_error());
diff --git a/src/image_compositing.cpp b/src/image_compositing.cpp
index a8f9bba3c..d6c8a3333 100644
--- a/src/image_compositing.cpp
+++ b/src/image_compositing.cpp
@@ -191,7 +191,20 @@ struct composite_visitor
           dy_(dy) {}
 
     template <typename T>
-    void operator() (T & dst) const;
+    void operator() (T & dst) const
+    {
+        throw std::runtime_error("Error: Composite with " + std::string(typeid(dst).name()) + " is not supported");
+    }
+
+    void operator()(image_rgba8 & dst) const
+    {
+        composite(dst, util::get<image_rgba8>(src_), mode_, opacity_, dx_, dy_);
+    }
+
+    void operator() (image_gray32f & dst) const
+    {
+        composite(dst, util::get<image_gray32f>(src_), mode_, opacity_, dx_, dy_);
+    }
 
   private:
     image_any const& src_;
@@ -199,26 +212,9 @@ struct composite_visitor
     float opacity_;
     int dx_;
     int dy_;
+
 };
 
-template <typename T>
-void composite_visitor::operator() (T & dst) const
-{
-    throw std::runtime_error("Error: Composite with " + std::string(typeid(dst).name()) + " is not supported");
-}
-
-template <>
-void composite_visitor::operator()<image_rgba8> (image_rgba8 & dst) const
-{
-    composite(dst, util::get<image_rgba8>(src_), mode_, opacity_, dx_, dy_);
-}
-
-template <>
-void composite_visitor::operator()<image_gray32f> (image_gray32f & dst) const
-{
-    composite(dst, util::get<image_gray32f>(src_), mode_, opacity_, dx_, dy_);
-}
-
 } // end ns
 
 template <>
diff --git a/src/load_map.cpp b/src/load_map.cpp
index f21708274..fcb04c003 100644
--- a/src/load_map.cpp
+++ b/src/load_map.cpp
@@ -200,7 +200,7 @@ void map_parser::parse_map(Map & map, xml_node const& node, std::string const& b
             {
                 map.set_background(*bgcolor);
             }
-            
+
             optional<std::string> image_filename = map_node.get_opt_attr<std::string>("background-image");
             if (image_filename)
             {
@@ -891,7 +891,7 @@ void map_parser::parse_symbolizer_base(symbolizer_base &sym, xml_node const& nod
 {
     set_symbolizer_property<symbolizer_base,double>(sym, keys::simplify_tolerance, node);
     set_symbolizer_property<symbolizer_base,double>(sym, keys::smooth, node);
-    set_symbolizer_property<symbolizer_base,boolean_type>(sym, keys::clip, node);
+    set_symbolizer_property<symbolizer_base,value_bool>(sym, keys::clip, node);
     set_symbolizer_property<symbolizer_base,composite_mode_e>(sym, keys::comp_op, node);
     set_symbolizer_property<symbolizer_base,transform_type>(sym, keys::geometry_transform, node);
     set_symbolizer_property<symbolizer_base,simplify_algorithm_e>(sym, keys::simplify_algorithm, node);
@@ -907,8 +907,8 @@ void map_parser::parse_point_symbolizer(rule & rule, xml_node const & node)
         point_symbolizer sym;
         parse_symbolizer_base(sym, node);
         set_symbolizer_property<symbolizer_base,double>(sym, keys::opacity, node);
-        set_symbolizer_property<symbolizer_base,boolean_type>(sym, keys::allow_overlap, node);
-        set_symbolizer_property<symbolizer_base,boolean_type>(sym, keys::ignore_placement, node);
+        set_symbolizer_property<symbolizer_base,value_bool>(sym, keys::allow_overlap, node);
+        set_symbolizer_property<symbolizer_base,value_bool>(sym, keys::ignore_placement, node);
         set_symbolizer_property<symbolizer_base,point_placement_enum>(sym, keys::point_placement_type, node);
         set_symbolizer_property<symbolizer_base,transform_type>(sym, keys::image_transform, node);
         if (file && !file->empty())
@@ -1011,9 +1011,9 @@ void map_parser::parse_markers_symbolizer(rule & rule, xml_node const& node)
         set_symbolizer_property<symbolizer_base,double>(sym, keys::offset, node);
         set_symbolizer_property<symbolizer_base,double>(sym, keys::width, node);
         set_symbolizer_property<symbolizer_base,double>(sym, keys::height, node);
-        set_symbolizer_property<symbolizer_base,boolean_type>(sym, keys::allow_overlap, node);
-        set_symbolizer_property<symbolizer_base,boolean_type>(sym, keys::avoid_edges, node);
-        set_symbolizer_property<symbolizer_base,boolean_type>(sym, keys::ignore_placement, node);
+        set_symbolizer_property<symbolizer_base,value_bool>(sym, keys::allow_overlap, node);
+        set_symbolizer_property<symbolizer_base,value_bool>(sym, keys::avoid_edges, node);
+        set_symbolizer_property<symbolizer_base,value_bool>(sym, keys::ignore_placement, node);
         set_symbolizer_property<symbolizer_base,color>(sym, keys::fill, node);
         set_symbolizer_property<symbolizer_base,transform_type>(sym, keys::image_transform, node);
         set_symbolizer_property<symbolizer_base,marker_placement_enum>(sym, keys::markers_placement_type, node);
@@ -1172,7 +1172,7 @@ void map_parser::parse_shield_symbolizer(rule & rule, xml_node const& node)
         set_symbolizer_property<symbolizer_base,double>(sym, keys::shield_dx, node);
         set_symbolizer_property<symbolizer_base,double>(sym, keys::shield_dy, node);
         set_symbolizer_property<symbolizer_base,double>(sym, keys::opacity, node);
-        set_symbolizer_property<symbolizer_base,mapnik::boolean_type>(sym, keys::unlock_image, node);
+        set_symbolizer_property<symbolizer_base,value_bool>(sym, keys::unlock_image, node);
 
         std::string file = node.get_attr<std::string>("file");
         if (file.empty())
@@ -1343,7 +1343,7 @@ void map_parser::parse_raster_symbolizer(rule & rule, xml_node const & node)
 
         // premultiplied status of image
         optional<mapnik::boolean_type> premultiplied = node.get_opt_attr<mapnik::boolean_type>("premultiplied");
-        if (premultiplied) put(raster_sym, keys::premultiplied, *premultiplied);
+        if (premultiplied) put(raster_sym, keys::premultiplied, bool(*premultiplied));
 
         bool found_colorizer = false;
         for ( auto const& css : node)
diff --git a/src/map.cpp b/src/map.cpp
index 9feb21688..e943ceeef 100644
--- a/src/map.cpp
+++ b/src/map.cpp
@@ -746,7 +746,7 @@ featureset_ptr Map::query_point(unsigned index, double x, double y) const
         else s << " (map has no layers)";
         throw std::out_of_range(s.str());
     }
-    return featureset_ptr();
+    return mapnik::make_empty_featureset();
 }
 
 featureset_ptr Map::query_map_point(unsigned index, double x, double y) const
diff --git a/src/palette.cpp b/src/palette.cpp
index 4c3807d1c..1fc5b8b21 100644
--- a/src/palette.cpp
+++ b/src/palette.cpp
@@ -65,16 +65,6 @@ rgba_palette::rgba_palette()
 #endif
 }
 
-const std::vector<rgb>& rgba_palette::palette() const
-{
-    return rgb_pal_;
-}
-
-const std::vector<unsigned>& rgba_palette::alphaTable() const
-{
-    return alpha_pal_;
-}
-
 bool rgba_palette::valid() const
 {
     return colors_ > 0;
diff --git a/src/text/formatting/layout.cpp b/src/text/formatting/layout.cpp
index ef908c569..9a5ca10aa 100644
--- a/src/text/formatting/layout.cpp
+++ b/src/text/formatting/layout.cpp
@@ -75,9 +75,9 @@ node_ptr layout_node::from_xml(xml_node const& xml, fontset_map const& fontsets)
     if (xml.has_attribute("text-ratio")) set_property_from_xml<double>(n->text_ratio, "text-ratio", xml);
     if (xml.has_attribute("wrap-width")) set_property_from_xml<double>(n->wrap_width, "wrap-width", xml);
     if (xml.has_attribute("wrap-character")) set_property_from_xml<std::string>(n->wrap_char, "wrap-character", xml);
-    if (xml.has_attribute("wrap-before")) set_property_from_xml<mapnik::boolean_type>(n->wrap_before, "wrap-before", xml);
-    if (xml.has_attribute("repeat-wrap-character")) set_property_from_xml<mapnik::boolean_type>(n->repeat_wrap_char, "repeat-wrap-character", xml);
-    if (xml.has_attribute("rotate-displacement")) set_property_from_xml<mapnik::boolean_type>(n->rotate_displacement, "rotate-displacement", xml);
+    if (xml.has_attribute("wrap-before")) set_property_from_xml<mapnik::value_bool>(n->wrap_before, "wrap-before", xml);
+    if (xml.has_attribute("repeat-wrap-character")) set_property_from_xml<mapnik::value_bool>(n->repeat_wrap_char, "repeat-wrap-character", xml);
+    if (xml.has_attribute("rotate-displacement")) set_property_from_xml<mapnik::value_bool>(n->rotate_displacement, "rotate-displacement", xml);
     if (xml.has_attribute("orientation")) set_property_from_xml<double>(n->orientation, "orientation", xml);
     if (xml.has_attribute("horizontal-alignment")) set_property_from_xml<horizontal_alignment_e>(n->halign, "horizontal-alignment", xml);
     if (xml.has_attribute("vertical-alignment")) set_property_from_xml<vertical_alignment_e>(n->valign, "vertical-alignment", xml);
diff --git a/src/text/text_properties.cpp b/src/text/text_properties.cpp
index 4e3f1d10d..db37f7e26 100644
--- a/src/text/text_properties.cpp
+++ b/src/text/text_properties.cpp
@@ -105,9 +105,9 @@ void text_symbolizer_properties::text_properties_from_xml(xml_node const& node)
     set_property_from_xml<value_double>(expressions.label_position_tolerance, "label-position-tolerance", node);
     set_property_from_xml<value_double>(expressions.minimum_padding, "minimum-padding", node);
     set_property_from_xml<value_double>(expressions.minimum_path_length, "minimum-path-length", node);
-    set_property_from_xml<boolean_type>(expressions.avoid_edges, "avoid-edges", node);
-    set_property_from_xml<boolean_type>(expressions.allow_overlap, "allow-overlap", node);
-    set_property_from_xml<boolean_type>(expressions.largest_bbox_only, "largest-bbox-only", node);
+    set_property_from_xml<value_bool>(expressions.avoid_edges, "avoid-edges", node);
+    set_property_from_xml<value_bool>(expressions.allow_overlap, "allow-overlap", node);
+    set_property_from_xml<value_bool>(expressions.largest_bbox_only, "largest-bbox-only", node);
     set_property_from_xml<value_double>(expressions.max_char_angle_delta, "max-char-angle-delta", node);
     set_property_from_xml<text_upright_e>(expressions.upright, "upright", node);
 }
@@ -217,9 +217,9 @@ void text_layout_properties::from_xml(xml_node const &node, fontset_map const& f
     set_property_from_xml<double>(text_ratio, "text-ratio", node);
     set_property_from_xml<double>(wrap_width, "wrap-width", node);
     set_property_from_xml<std::string>(wrap_char, "wrap-character", node);
-    set_property_from_xml<boolean_type>(wrap_before, "wrap-before", node);
-    set_property_from_xml<boolean_type>(repeat_wrap_char, "repeat-wrap-character", node);
-    set_property_from_xml<boolean_type>(rotate_displacement, "rotate-displacement", node);
+    set_property_from_xml<value_bool>(wrap_before, "wrap-before", node);
+    set_property_from_xml<value_bool>(repeat_wrap_char, "repeat-wrap-character", node);
+    set_property_from_xml<value_bool>(rotate_displacement, "rotate-displacement", node);
     set_property_from_xml<double>(orientation, "orientation", node);
     set_property_from_xml<vertical_alignment_e>(valign, "vertical-alignment", node);
     set_property_from_xml<horizontal_alignment_e>(halign, "horizontal-alignment", node);
diff --git a/src/value.cpp b/src/value.cpp
index a3c8770cc..b5ad606c7 100644
--- a/src/value.cpp
+++ b/src/value.cpp
@@ -673,7 +673,7 @@ struct convert<std::string>
 
     std::string operator()(value_null const&) const
     {
-        return std::string();
+        return std::string("");
     }
 };
 
@@ -708,7 +708,7 @@ struct to_unicode_impl
 
     value_unicode_string operator()(value_null const&) const
     {
-        return value_unicode_string();
+        return value_unicode_string("");
     }
 };
 
diff --git a/src/xml_tree.cpp b/src/xml_tree.cpp
index 2cc2c6adc..cd6cdaca3 100644
--- a/src/xml_tree.cpp
+++ b/src/xml_tree.cpp
@@ -70,6 +70,7 @@ DEFINE_NAME_TRAIT( double, "double")
 DEFINE_NAME_TRAIT( float, "float")
 DEFINE_NAME_TRAIT( unsigned, "unsigned")
 DEFINE_NAME_TRAIT( int, "int")
+DEFINE_NAME_TRAIT( bool, "bool")
 DEFINE_NAME_TRAIT( boolean_type, "boolean_type")
 #ifdef BIGINT
 DEFINE_NAME_TRAIT( mapnik::value_integer, "long long" )
@@ -412,6 +413,7 @@ std::string xml_node::line_to_string() const
 #define compile_get_value(T) template T xml_node::get_value<T>() const
 
 compile_get_opt_attr(boolean_type);
+compile_get_opt_attr(mapnik::value_bool);
 compile_get_opt_attr(std::string);
 compile_get_opt_attr(int);
 compile_get_opt_attr(unsigned);
diff --git a/utils/pgsql2sqlite/pgsql2sqlite.hpp b/utils/pgsql2sqlite/pgsql2sqlite.hpp
index e339a8f58..9de886732 100644
--- a/utils/pgsql2sqlite/pgsql2sqlite.hpp
+++ b/utils/pgsql2sqlite/pgsql2sqlite.hpp
@@ -352,23 +352,23 @@ void pgsql2sqlite(Connection conn,
                     break;
                 }
                 case 23:
-                    output_rec.push_back(sqlite::value_type(int4net(buf)));
+                    output_rec.emplace_back(int4net(buf));
                     break;
                 case 21:
-                    output_rec.push_back(sqlite::value_type(int2net(buf)));
+                    output_rec.emplace_back(int(int2net(buf)));
                     break;
                 case 700:
                 {
                     float val;
                     float4net(val,buf);
-                    output_rec.push_back(sqlite::value_type(val));
+                    output_rec.emplace_back(double(val));
                     break;
                 }
                 case 701:
                 {
                     double val;
                     float8net(val,buf);
-                    output_rec.push_back(sqlite::value_type(val));
+                    output_rec.emplace_back(val);
                     break;
                 }
                 case 1700:
@@ -377,7 +377,7 @@ void pgsql2sqlite(Connection conn,
                     double val;
                     if (mapnik::util::string2double(str,val))
                     {
-                        output_rec.push_back(sqlite::value_type(val));
+                        output_rec.emplace_back(val);
                     }
                     break;
                 }