@@ -506,7 +506,7 @@ class LearnerND(BaseLearner):

         if self.vdim > 1:

             raise NotImplementedError('holoviews currently does not support',

                                       '3D surface plots in bokeh.')

-        if len(self.ndim) != 2:

+        if self.ndim != 2:

             raise NotImplementedError("Only 2D plots are implemented: You can "

                                       "plot a 2D slice with 'plot_slice'.")

         x, y = self._bbox

@@ -516,7 +516,9 @@ class LearnerND(BaseLearner):

             if n is None:

                 # Calculate how many grid points are needed.

                 # factor from A=√3/4 * a² (equilateral triangle)

-                n = int(0.658 / np.sqrt(np.min(self.tri.volumes())))

+                scale_factor = np.product(np.diag(self._transform))

+                a_sq = np.sqrt(np.min(self.tri.volumes()) * scale_factor)

+                n = max(10, int(0.658 / a_sq))

             xs = ys = np.linspace(0, 1, n)

             xs = xs * (x[1] - x[0]) + x[0]

@@ -585,7 +587,9 @@ class LearnerND(BaseLearner):

             if n is None:

                 # Calculate how many grid points are needed.

                 # factor from A=√3/4 * a² (equilateral triangle)

-                n = int(0.658 / np.sqrt(np.min(self.tri.volumes())))

+                scale_factor = np.product(np.diag(self._transform))

+                a_sq = np.sqrt(np.min(self.tri.volumes()) * scale_factor)

+                n = max(10, int(0.658 / a_sq))

             xs = ys = np.linspace(0, 1, n)

             xys = [xs[:, None], ys[None, :]]

@@ -780,7 +784,7 @@ class LearnerND(BaseLearner):

                 plot = plot * self.plot_isoline(level=l, n=-1)

             return plot

-        vertices, lines = self.self._get_iso(level, which='line')

+        vertices, lines = self._get_iso(level, which='line')

         paths = [[vertices[i], vertices[j]] for i, j in lines]

         contour = hv.Path(paths)