diff --git a/SimPEG/Models.py b/SimPEG/Models.py
index f69b749c..65cfdeee 100644
--- a/SimPEG/Models.py
+++ b/SimPEG/Models.py
@@ -31,5 +31,5 @@ class Model(np.ndarray):
     @property
     def transformDeriv(self):
         if getattr(self, '_transformDeriv', None) is None:
-            self.deriv = self.mapping.deriv(self.view(np.ndarray))
-        return self.deriv
+            self._transformDeriv = self.mapping.deriv(self.view(np.ndarray))
+        return self._transformDeriv
diff --git a/SimPEG/Utils/PropMaps.py b/SimPEG/Utils/PropMaps.py
new file mode 100644
index 00000000..e4c49407
--- /dev/null
+++ b/SimPEG/Utils/PropMaps.py
@@ -0,0 +1,177 @@
+from SimPEG import Utils, Maps
+
+class Property(object):
+
+    name           = ''
+    doc            = ''
+    # mappingPair    = None
+
+    defaultVal     = None
+    defaultMap     = None
+    defaultInvProp = False
+
+    def __init__(self, doc, **kwargs):
+        # Set the default after all other params are set
+        self.doc = doc
+        Utils.setKwargs(self, **kwargs)
+
+    def _getMapProperty(self):
+        prop = self
+        def fget(self):
+            return getattr(self, '_%sMap'%prop.name, prop.defaultMap)
+        def fset(self, val):
+            # TODO: Check if the mapping can be correct
+            setattr(self, '_%sMap'%prop.name, val)
+        return property(fget=fget, fset=fset, doc=prop.doc)
+
+    def _getIndexProperty(self):
+        prop = self
+        def fget(self):
+            return getattr(self, '_%sIndex'%prop.name, slice(None))
+        def fset(self, val):
+            setattr(self, '_%sIndex'%prop.name, val)
+        return property(fget=fget, fset=fset, doc=prop.doc)
+
+    def _getProperty(self):
+        prop = self
+        def fget(self):
+            mapping = getattr(self, '%sMap'%prop.name)
+            if mapping is None:
+                return prop.defaultVal
+            m       = getattr(self, '%sModel'%prop.name)
+            return mapping * m
+        return property(fget=fget)
+
+    def _getModelDerivProperty(self):
+        prop = self
+        def fget(self):
+            m       = getattr(self, '%sModel'%prop.name)
+            mapping = getattr(self, '%sMap'%prop.name)
+            if mapping is None:
+                return None
+            return mapping.deriv( m )
+        return property(fget=fget)
+
+    def _getModelProperty(self):
+        prop = self
+        def fget(self):
+            mapping = getattr(self, '%sMap'%prop.name)
+            if mapping is None:
+                return None
+            index = getattr(self.propMap, '_%sIndex'%prop.name, slice(None))
+            return self.vector[index]
+        return property(fget=fget)
+
+    def _getModelMapProperty(self):
+        prop = self
+        def fget(self):
+            return getattr(self.propMap, '_%sMap'%prop.name, prop.defaultMap)
+        return property(fget=fget)
+
+
+
+class PropModel(object):
+    def __init__(self, propMap, vector):
+        self.propMap = propMap
+        self.vector  = vector
+
+    # TODO: nP
+
+
+_PROPMAPCLASSREGISTRY = {}
+
+class _PropMapMetaClass(type):
+    def __new__(cls, name, bases, attrs):
+        assert name.endswith('PropMap'), 'Please use convention: ___PropMap, e.g. ElectromagneticPropMap'
+        _properties = {}
+        for base in bases:
+            for baseProp in getattr(base, '_properties', {}):
+                _properties[baseProp] = base._properties[baseProp]
+        keys = [key for key in attrs]
+        for attr in keys:
+            if isinstance(attrs[attr], Property):
+                attrs[attr].name = attr
+                attrs[attr + 'Map'  ] = attrs[attr]._getMapProperty()
+                attrs[attr + 'Index'] = attrs[attr]._getIndexProperty()
+                _properties[attr] = attrs[attr]
+                attrs.pop(attr)
+
+        attrs['_properties'] = _properties
+
+        newClass = super(_PropMapMetaClass, cls).__new__(cls, name, bases, attrs)
+
+        newClass.PropModel = cls.createPropModelClass(newClass, name, _properties)
+
+        _PROPMAPCLASSREGISTRY[name] = newClass
+        return newClass
+
+    def createPropModelClass(self, name, _properties):
+
+        attrs = dict()
+
+        for attr in _properties:
+            prop = _properties[attr]
+
+            attrs[attr          ] = prop._getProperty()
+            attrs[attr + 'Map'  ] = prop._getModelMapProperty()
+            attrs[attr + 'Model'] = prop._getModelProperty()
+            attrs[attr + 'Deriv'] = prop._getModelDerivProperty()
+
+        return type(name.replace('PropMap', 'PropModel'), (PropModel, ), attrs)
+
+
+
+
+
+class PropMap(object):
+    __metaclass__ = _PropMapMetaClass
+
+    def __init__(self, ):
+        """
+            PropMap takes a multi parameter model and maps it to the equivalent PropModel
+        """
+        pass
+
+    def __call__(self, vec):
+        return self.PropModel(self, vec)
+
+
+class MyPropMap(PropMap):
+    sigma = Property("Electrical Conductivity", defaultInvProp=True)
+    # rho   = InveseProperty(sigma)
+
+class My2PropMap(MyPropMap):
+    mu    = Property("Electrical Conductivity", defaultVal=4e-10)
+
+
+if __name__ == '__main__':
+
+
+    from SimPEG import Mesh
+    import numpy as np
+
+    expMap = Maps.ExpMap(Mesh.TensorMesh((3,)))
+    print expMap.nP
+
+    # propMap = MyPropMap([('sigma', expMap), ('mu', IMap)], indices={'sigma':[1,2,3,4,7,8]})
+    propMap = MyPropMap()
+    print [n for n in dir(propMap) if n[0] is not '_']
+    propMap = My2PropMap()
+    print [n for n in dir(propMap) if n[0] is not '_']
+
+    propMap.sigmaMap = expMap
+
+    print propMap.sigmaMap
+    print propMap.sigmaIndex
+
+    mod = propMap(np.r_[1,2,3])
+    print [n for n in dir(mod) if n[0] is not '_']
+    print mod.sigmaModel
+    print mod.sigma
+    print mod.sigmaMap
+    print mod.sigmaDeriv
+
+    print mod.mu
+    print mod.muMap
+    print mod.muModel
+    print mod.muDeriv
diff --git a/SimPEG/Utils/codeutils.py b/SimPEG/Utils/codeutils.py
index 1399c1b5..0ba57b2e 100644
--- a/SimPEG/Utils/codeutils.py
+++ b/SimPEG/Utils/codeutils.py
@@ -58,9 +58,11 @@ def hook(obj, method, name=None, overwrite=False, silent=False):
         print 'Method '+name+' was not overwritten.'
 
 
-def setKwargs(obj, **kwargs):
+def setKwargs(obj, ignore=[],  **kwargs):
     """Sets key word arguments (kwargs) that are present in the object, throw an error if they don't exist."""
     for attr in kwargs:
+        if attr in ignore:
+            continue
         if hasattr(obj, attr):
             setattr(obj, attr, kwargs[attr])
         else: