diff --git a/gridfinder/__init__.py b/gridfinder/__init__.py
index f908a6f..a1f2c92 100644
--- a/gridfinder/__init__.py
+++ b/gridfinder/__init__.py
@@ -1,7 +1,14 @@
 from importlib.metadata import version
 
 from gridfinder.gridfinder import get_targets_costs, optimise
-from gridfinder.post import accuracy, raster_to_lines, thin, threshold, threshold_arr
+from gridfinder.post import (
+    accuracy,
+    raster_to_lines,
+    thin,
+    thin_arr,
+    threshold,
+    threshold_arr,
+)
 from gridfinder.prepare import (
     clip_rasters,
     create_filter,
@@ -21,6 +28,7 @@
     "threshold",
     "threshold_arr",
     "thin",
+    "thin_arr",
     "raster_to_lines",
     "accuracy",
     "clip_rasters",
diff --git a/gridfinder/post.py b/gridfinder/post.py
index c05da2c..394be6d 100644
--- a/gridfinder/post.py
+++ b/gridfinder/post.py
@@ -59,11 +59,15 @@ def thin(guess_in: Pathy) -> tuple[np.ndarray, Affine]:
     with rs.open(guess_in) as ds:
         guess_arr = ds.read(1)
         affine = ds.transform
+    guess_skel = thin_arr(guess_arr)
+    return guess_skel, affine
+
 
-    guess_skel = skeletonize(guess_arr)
+def thin_arr(guess: np.ndarray) -> np.ndarray:
+    guess_skel = skeletonize(guess)
     guess_skel = guess_skel.astype("int32")
+    return guess_skel
 
-    return guess_skel, affine
 
 
 def raster_to_lines(guess_skel_in: Pathy) -> gpd.GeoDataFrame: