@@ -580,33 +580,32 @@ class Learner1D(BaseLearner):

         loss = mapping[ival]

         return finite_loss(ival, loss, self._scale[0])

-    def plot(self, *, scatter_or_line=None):

+    def plot(self, *, scatter_or_line="scatter"):

         """Returns a plot of the evaluated data.

+        Parameters

+        ----------

+        scatter_or_line : str, default: "scatter"

+            Plot as a scatter plot ("scatter") or a line plot ("line").

+

         Returns

         -------

-        plot : `holoviews.element.Scatter` (if vdim=1)\

-               else `holoviews.element.Path`

+        plot : `holoviews.Scatter`, `holoviews.Path`, or `holoviews.Overlay`

             Plot of the evaluated data.

-        scatter_or_line : str, optional

-            Plot as a scatter plot ("scatter") or a line plot ("line").

-            By default a line plot will be chosen if the data consists of

-            vectors, otherwise it is a scatter plot.

         """

+        if scatter_or_line not in ("scatter", "line"):

+            raise ValueError("scatter_or_line must be 'scatter' or 'line'")

         hv = ensure_holoviews()

         xs, ys = zip(*sorted(self.data.items())) if self.data else ([], [])

-        if self.vdim == 1:

-            if scatter_or_line is None or scatter_or_line == "scatter":

-                p = hv.Path([]) * hv.Scatter((xs, ys))

-            else:

-                p = hv.Path((xs, ys)) * hv.Scatter()

-        else:

-            if scatter_or_line is None or scatter_or_line == "line":

-                p = hv.Path((xs, ys)) * hv.Scatter([])

+        if scatter_or_line == "scatter":

+            if self.vdim == 1:

+                p = hv.Scatter((xs, ys))

             else:

                 scatters = [hv.Scatter((xs, _ys)) for _ys in np.transpose(ys)]

-                p = hv.Path([]) * hv.Overlay(scatters)

+                p = hv.Overlay(scatters)

+        else:

+            p = hv.Path((xs, ys))

         # Plot with 5% empty margins such that the boundary points are visible

         margin = 0.05 * (self.bounds[1] - self.bounds[0])