diff --git a/swmmanywhere/graph_utilities.py b/swmmanywhere/graph_utilities.py
index da683a12..9daa7ae9 100644
--- a/swmmanywhere/graph_utilities.py
+++ b/swmmanywhere/graph_utilities.py
@@ -537,13 +537,14 @@ def __call__(self, G: nx.Graph, **kwargs) -> nx.Graph:
         weights = [1, 0, 0, 1]
 
         # Calculate weights
-        chahinian_weights = [
-            {(u,v): np.interp(d['surface_slope'] * 100,
+        chahinian_weights = {
+            (u,v): np.interp(d['surface_slope'] * 100,
                                           angle_points,
                                           weights,
                                           left=1.0,
-                                          right=1.0)}
-             for u, v, d in G.edges(data=True)]
+                                          right=1.0)
+            for u, v, d in G.edges(data=True)}
+             
         
         # Update graph
         nx.set_edge_attributes(G, chahinian_weights, 'chahinian_slope')