diff --git a/SimPEG/Maps.py b/SimPEG/Maps.py
index dde3e752..4b219f22 100644
--- a/SimPEG/Maps.py
+++ b/SimPEG/Maps.py
@@ -68,8 +68,8 @@ class IdentityMap(object):
 
     def _assertMatchesPair(self, pair):
         assert (isinstance(self, pair) or
-            isinstance(self, ComboMap) and isinstance(self.models[0], pair)
-            ), "Model object must be an instance of a %s class."%(pair.__name__)
+            isinstance(self, ComboMap) and isinstance(self.maps[0], pair)
+            ), "Mapping object must be an instance of a %s class."%(pair.__name__)
 
 class NonLinearMap(object):
     """
@@ -335,17 +335,17 @@ class ActiveCells(IdentityMap):
         return self.P
 
 class ComboMap(IdentityMap):
-    """Combination of various models."""
+    """Combination of various maps."""
 
-    def __init__(self, mesh, models, **kwargs):
+    def __init__(self, mesh, maps, **kwargs):
         IdentityMap.__init__(self, mesh, **kwargs)
 
-        self.models = []
-        for m in models:
+        self.maps = []
+        for m in maps:
             if not isinstance(m, IdentityMap):
-                self.models += [m(mesh, **kwargs)]
+                self.maps += [m(mesh, **kwargs)]
             else:
-                self.models += [m]
+                self.maps += [m]
 
     @property
     def nP(self):
@@ -353,19 +353,19 @@ class ComboMap(IdentityMap):
 
            The number of cells in the
            last dimension of the mesh."""
-        return self.models[-1].nP
+        return self.maps[-1].nP
 
     def transform(self, m):
-        for model in reversed(self.models):
-            m = model.transform(m)
+        for map_i in reversed(self.maps):
+            m = map_i.transform(m)
         return m
 
     def transformDeriv(self, m):
         deriv = 1
         mi = m
-        for model in reversed(self.models):
-            deriv = model.transformDeriv(mi) * deriv
-            mi = model.transform(mi)
+        for map_i in reversed(self.maps):
+            deriv = map_i.transformDeriv(mi) * deriv
+            mi = map_i.transform(mi)
         return deriv
 
 if __name__ == '__main__':
diff --git a/SimPEG/Problem.py b/SimPEG/Problem.py
index f88fdb9a..2175c24d 100644
--- a/SimPEG/Problem.py
+++ b/SimPEG/Problem.py
@@ -1,5 +1,5 @@
 import Utils, Survey, numpy as np, scipy.sparse as sp
-import Maps
+import Maps, Mesh
 
 class BaseProblem(object):
     """
@@ -18,6 +18,7 @@ class BaseProblem(object):
 
     def __init__(self, mesh, mapping=None, **kwargs):
         Utils.setKwargs(self, **kwargs)
+        assert isinstance(mesh, Mesh.BaseMesh), "mesh must be a SimPEG.Mesh object."
         self.mesh = mesh
         self.mapping = mapping or Maps.IdentityMap(mesh)
         self.mapping._assertMatchesPair(self.mapPair)
diff --git a/SimPEG/Tests/test_maps.py b/SimPEG/Tests/test_maps.py
index abd5701f..3b417fe6 100644
--- a/SimPEG/Tests/test_maps.py
+++ b/SimPEG/Tests/test_maps.py
@@ -14,24 +14,24 @@ class MapTests(unittest.TestCase):
         self.mesh2 = Mesh.TensorMesh([a, b], x0=np.array([3, 5]))
         self.mesh22 = Mesh.TensorMesh([b, a], x0=np.array([3, 5]))
 
-    def test_modelTransforms(self):
+    def test_transforms(self):
         for M in dir(Maps):
             try:
-                model = getattr(Maps, M)(self.mesh2)
-                assert isinstance(model, Maps.BaseModel)
+                maps = getattr(Maps, M)(self.mesh2)
+                assert isinstance(maps, Maps.BaseModel)
             except Exception, e:
                 continue
-            self.assertTrue(model.test())
+            self.assertTrue(maps.test())
 
     def test_Mesh2MeshMap(self):
-        model = Maps.Mesh2Mesh([self.mesh22, self.mesh2])
-        self.assertTrue(model.test())
+        maps = Maps.Mesh2Mesh([self.mesh22, self.mesh2])
+        self.assertTrue(maps.test())
 
     def test_comboMaps(self):
         combos = [(Maps.ExpMap, Maps.Vertical1DMap)]
         for combo in combos:
-            model = Maps.ComboMap(self.mesh2, combo)
-            self.assertTrue(model.test())
+            maps = Maps.ComboMap(self.mesh2, combo)
+            self.assertTrue(maps.test())
 
 
 if __name__ == '__main__':