+    def __new__(cls, coordinates):
+        if isinstance(coordinates, Mapping):
+            coordinates = coordinates.items()
+        self = object().__new__(cls)
+        self._coordinates = OrderedDict()
+        for symbol, coordinate in sorted(coordinates,
+                key=lambda item: item[0].sortkey()):
+            if not isinstance(symbol, Symbol):
+                raise TypeError('symbols must be Symbol instances')
+            if not isinstance(coordinate, numbers.Real):
+                raise TypeError('coordinates must be real numbers')
+            self._coordinates[symbol] = coordinate
+        return self