diff --git a/qgis_plugin/qgismappy/utils.py b/qgis_plugin/qgismappy/utils.py
new file mode 100644
index 0000000..b70afd0
--- /dev/null
+++ b/qgis_plugin/qgismappy/utils.py
@@ -0,0 +1,55 @@
+from qgis.PyQt.QtCore import NULL
+from qgis.core import QgsCategorizedSymbolRenderer, QgsSymbol, QgsRendererCategory
+
+
+def resetCategoriesIfNeeded(layer, units_field, unassigned=True):
+    prev_rend = layer.renderer()
+
+    if not isinstance(prev_rend, QgsCategorizedSymbolRenderer):
+        renderer = QgsCategorizedSymbolRenderer(units_field)
+        layer.setRenderer(renderer)
+    else:
+        renderer = prev_rend
+
+    prev_cats = renderer.categories()
+    id = layer.fields().indexFromName(units_field)
+    uniques = list(layer.uniqueValues(id))
+    uniques_clean = []
+
+    for u in uniques:
+        if u not in [None, NULL]:
+            uniques_clean.append(u)
+
+    values = sorted(uniques_clean)
+
+    if unassigned:
+        if None in uniques or NULL in uniques:
+            values.append("")
+
+    categories = []
+
+    for current, value in enumerate(values):
+
+        already_in = False
+        for prev in prev_cats:
+            if prev.value() == value:
+                already_in = True
+                continue
+
+        if not already_in:
+            if value =="":
+                name = "Unassigned"
+            else:
+                name = str(value)
+            symbol = QgsSymbol.defaultSymbol(layer.geometryType())
+            category = QgsRendererCategory(value, symbol, name)
+            categories.append(category)
+
+    for cat in categories:
+        renderer.addCategory(cat)
+
+    # layer.setRenderer(renderer)
+    layer.rendererChanged.emit()
+    layer.dataSourceChanged.emit()
+
+    layer.triggerRepaint()
\ No newline at end of file