diff --git a/process/subprocesses/_12_neighbourhood_analysis.py b/process/subprocesses/_12_neighbourhood_analysis.py
index b7ee83fc..6165962b 100644
--- a/process/subprocesses/_12_neighbourhood_analysis.py
+++ b/process/subprocesses/_12_neighbourhood_analysis.py
@@ -33,6 +33,7 @@
     cal_dist_node_to_nearest_pois,
     create_full_nodes,
     create_pdna_net,
+    filter_ids,
     spatial_join_index_to_gdf,
 )
 from tqdm import tqdm
@@ -85,9 +86,7 @@ def main():
         print('  - Set up simple nodes')
         gdf_nodes = ox.graph_to_gdfs(G_proj, nodes=True, edges=False)
         # associate nodes with id
-        gdf_nodes = spatial_join_index_to_gdf(
-            gdf_nodes, grid, right_index_name='grid_id', join_type='within',
-        )
+        gdf_nodes = spatial_join_index_to_gdf(gdf_nodes, grid, dropna=False)
         # keep only the unique node id column
         gdf_nodes = gdf_nodes[['grid_id', 'geometry']]
         # drop any nodes which are na
@@ -258,42 +257,17 @@ def main():
     samplePointsData = gpd.read_file(gpkg, layer='urban_sample_points')
     # create 'grid_id' for sample point, if it not exists
     if 'grid_id' not in samplePointsData.columns:
-        samplePointsData = spatial_join_index_to_gdf(
-            samplePointsData,
-            grid,
-            right_index_name='grid_id',
-            join_type='within',
-        )
-    print(
-        'Restrict sample points to those not located in grids with a population below '
+        samplePointsData = spatial_join_index_to_gdf(samplePointsData, grid)
+    samplePointsData = filter_ids(
+        df=samplePointsData,
+        query=f"""grid_id not in {list(grid.query(f'pop_est < {population["pop_min_threshold"]}').index.values)}""",
+        message='Restrict sample points to those not located in grids with a population below '
         f"the minimum threshold value ({population['pop_min_threshold']})...",
-    ),
-    below_minimum_pop_ids = list(
-        grid.query(
-            f'pop_est < {population["pop_min_threshold"]}',
-        ).index.values,
-    )
-    sample_point_length_pre_discard = len(samplePointsData)
-    samplePointsData = samplePointsData[
-        ~samplePointsData.grid_id.isin(below_minimum_pop_ids)
-    ]
-    sample_point_length_post_discard = len(samplePointsData)
-    print(
-        f'  {sample_point_length_pre_discard - sample_point_length_post_discard} sample points discarded, '
-        f'leaving {sample_point_length_post_discard} remaining.',
     )
-    print(
-        'Restrict sample points to those with two associated sample nodes...',
-    ),
-    sample_point_length_pre_discard = len(samplePointsData)
-    samplePointsData = samplePointsData.query(
-        f'n1 in {list(gdf_nodes_simple.index.values)} '
-        f'and n2 in {list(gdf_nodes_simple.index.values)}',
-    )
-    sample_point_length_post_discard = len(samplePointsData)
-    print(
-        f'  {sample_point_length_pre_discard - sample_point_length_post_discard} sample points discarded, '
-        f'leaving {sample_point_length_post_discard} remaining.',
+    samplePointsData = filter_ids(
+        df=samplePointsData,
+        query=f"""n1 in {list(gdf_nodes_simple.index.values)} and n2 in {list(gdf_nodes_simple.index.values)}""",
+        message='Restrict sample points to those with two associated sample nodes...',
     )
     samplePointsData.set_index('point_id', inplace=True)
     distance_names = list(gdf_nodes_poi_dist.columns)
diff --git a/process/subprocesses/setup_sp.py b/process/subprocesses/setup_sp.py
index b8865ac3..fb7f642e 100644
--- a/process/subprocesses/setup_sp.py
+++ b/process/subprocesses/setup_sp.py
@@ -17,7 +17,7 @@
 
 
 def spatial_join_index_to_gdf(
-    gdf, join_gdf, right_index_name, join_type='within',
+    gdf, join_gdf, join_type='within', dropna=True,
 ):
     """Append to a geodataframe the named index of another using spatial join.
 
@@ -25,8 +25,8 @@ def spatial_join_index_to_gdf(
     ----------
     gdf: GeoDataFrame
     join_gdf: GeoDataFrame
-    right_index_name: str (default: None)
-    join_tyoe: str (default 'within')
+    join_type: str (default 'within')
+    dropna: True
 
     Returns
     -------
@@ -34,12 +34,40 @@ def spatial_join_index_to_gdf(
     """
     gdf_columns = list(gdf.columns)
     gdf = gpd.sjoin(gdf, join_gdf, how='left', predicate=join_type)
-    if right_index_name is not None:
-        gdf = gdf[gdf_columns + ['index_right']]
-        gdf.columns = gdf_columns + [right_index_name]
+    gdf = gdf[gdf_columns + ['index_right']]
+    gdf.columns = gdf_columns + [join_gdf.index.name]
+    if dropna:
+        gdf = gdf[~gdf[join_gdf.index.name].isna()]
+        gdf[join_gdf.index.name] = gdf[join_gdf.index.name].astype(
+            join_gdf.index.dtype,
+        )
     return gdf
 
 
+def filter_ids(df, query, message):
+    """Pandas query designed to filter and report feedback on counts before and after query.
+
+    Parameters
+    ----------
+    df: DataFrame
+    query: str Pandas query string
+    message: str An informative message to print describing query in plain language
+
+    Returns
+    -------
+    DataFrame
+    """
+    print(message)
+    pre_discard = len(df)
+    df = df.query(query)
+    post_discard = len(df)
+    print(
+        f'  {pre_discard - post_discard} sample points discarded, '
+        f'leaving {post_discard} remaining.',
+    )
+    return df
+
+
 def create_pdna_net(gdf_nodes, gdf_edges, predistance=500):
     """Create pandana network to prepare for calculating the accessibility to destinations The network is comprised of a set of nodes and edges.