diff --git a/api/s32_virtual_district.py b/api/s32_virtual_district.py
index 85b8585..6ce4682 100644
--- a/api/s32_virtual_district.py
+++ b/api/s32_virtual_district.py
@@ -1,6 +1,16 @@
 from .database import *
 from .s0_base import get_node_links
 
+
+def _polygon_to_nodes(polygon: str) -> list[tuple[float, float]]:
+    boundary = polygon.removeprefix('POLYGON((').removesuffix('))').split(',')
+    xys = []
+    for pt in boundary:
+        xy = pt.split(' ')
+        xys.append((float(xy[0]), float(xy[1])))
+    return xys
+
+
 def calculate_virtual_district(name: str, centers: list[str]) -> dict[str, Any]:
     write(name, 'drop table if exists vd_graph')
     write(name, 'create table vd_graph (id serial, source integer, target integer, cost numeric)')
@@ -71,15 +81,8 @@ def calculate_virtual_district(name: str, centers: list[str]) -> dict[str, Any]:
         # TODO: check none
         boundary = read(name, f'select st_astext(st_convexhull(st_collect(array(select coord from coordinates where node in (select * from vd_{center}))))) as boundary' )['boundary']
         # write(name, f"insert into virtual_district (id, center, boundary) values ('vd_{center}', '{center}', st_geomfromtext('{boundary}'))")
-
-        outlines = str(boundary).removeprefix('POLYGON((').removesuffix('))').split(',')
-        outline_tuples = []
-        for pt in outlines:
-            xy = pt.split(' ')
-            outline_tuples.append((float(xy[0]), float(xy[1])))
-
-        vd = { 'center': center, 'nodes': value, 'boundary': outline_tuples }
-        vds.append(vd)
+        xys = _polygon_to_nodes(boundary)
+        vds.append({ 'center': center, 'nodes': value, 'boundary': xys })
 
         write(name, f'drop table vd_{center}')