diff --git a/WrightTools/data/_data.py b/WrightTools/data/_data.py
index 62624584..6bc0e22d 100644
--- a/WrightTools/data/_data.py
+++ b/WrightTools/data/_data.py
@@ -1263,10 +1263,14 @@ def level(self, channel, axis, npts, *, verbose=True):
     def map_variable(
         self, variable, points, input_units="same", *, name=None, parent=None, verbose=True
     ) -> "Data":
-        """Map points of an axis to new points using linear interpolation.
+        """
+        Map points of an axis to new points using linear interpolation.
 
         Out-of-bounds points are written nan.
 
+        Non-mapped variables are kept in the data object only if they are
+        orthogonal to the mapped variable (see `kit.orthogonal`).
+
         Parameters
         ----------
         variable : string