diff --git a/src/xtgeo/grid3d/_gridprop_op1.py b/src/xtgeo/grid3d/_gridprop_op1.py
index c768532f2..07095d196 100644
--- a/src/xtgeo/grid3d/_gridprop_op1.py
+++ b/src/xtgeo/grid3d/_gridprop_op1.py
@@ -1,5 +1,8 @@
 """Various grid property operations"""
+# pylint: disable=protected-access
+from __future__ import annotations
 
+from typing import TYPE_CHECKING, List, Optional, Tuple, Union
 
 import numpy as np
 
@@ -12,11 +15,20 @@
 
 logger = xtg.functionlogger(__name__)
 
+if TYPE_CHECKING:
+    from xtgeo.grid3d import Grid, GridProperty
+    from xtgeo.xyz import Polygons
 
-# pylint: disable=protected-access
 
+XYCoordinate = Tuple[Union[float, int], Union[float, int]]
+XYCoordList = List[List[List[XYCoordinate]]]
+ValueList = List[List[Union[float, int]]]
+XYValueLists = Tuple[XYCoordList, ValueList]
 
-def get_xy_value_lists(self, **kwargs):
+
+def get_xy_value_lists(
+    self, grid: Optional[Union[Grid, GridProperty]] = None, mask: Optional[bool] = None
+) -> XYValueLists:
     """Get values for webportal format
 
     Two cells:
@@ -28,11 +40,6 @@ def get_xy_value_lists(self, **kwargs):
     will have a -999 value.
 
     """
-
-    grid = kwargs.get("grid", None)
-
-    mask = kwargs.get("mask", True)
-
     if grid is None:
         raise RuntimeError("Missing grid object")
 
@@ -76,11 +83,17 @@ def get_xy_value_lists(self, **kwargs):
     return coordlist, valuelist
 
 
-def operation_polygons(self, poly, value, opname="add", inside=True):
+def operation_polygons(
+    self,
+    poly: Polygons,
+    value: Union[float, int],
+    opname: str = "add",
+    inside: bool = True,
+) -> None:
     """A generic function for doing operations restricted to inside
     or outside polygon(s).
-    """
 
+    """
     grid = self.geometry
     grid._xtgformat1()
 
@@ -135,7 +148,7 @@ def operation_polygons(self, poly, value, opname="add", inside=True):
     elif opname == "div":
         # Dividing a map of zero is always a hazzle; try to obtain 0.0
         # as result in these cases
-        if 0.0 in value:
+        if value == 0.0:
             xtg.warn(
                 "Dividing a surface with value or surface with zero "
                 "elements; may get unexpected results, try to "