Merge pull request matplotlib#31016 from sanrishi/fix-contour-levels-doc

Doc: Clarify default levels behavior in contour/contourf

Author: timhoffm

lib/matplotlib/contour.py

@@ -1486,16 +1486,22 @@ def _initialize_x_y(self, z):
 levels : int or array-like, optional
     Determines the number and positions of the contour lines / regions.
 
-    If an int *n*, use `~matplotlib.ticker.MaxNLocator`, which tries
-    to automatically choose no more than *n+1* "nice" contour levels
-    between minimum and maximum numeric values of *Z*.
+    If an int *n*, use `~matplotlib.ticker.MaxNLocator`, which tries to
+    automatically choose no more than *n+2* "nice" contour level boundaries
+    between the minimum and maximum numeric values of *Z*. These boundaries
+    define where lines are drawn (for `contour`) or where filled regions
+    are separated (for `contourf`).
 
     If not given, a reasonable default is chosen; for linear scales,
     *n*=7 is the default.
 
     If array-like, draw contour lines at the specified levels.
     The values must be in increasing order.
 
+    If not specified, a reasonable default is automatically chosen. For
+    linear scales, this corresponds to *levels=7*. For logarithmic
+    scales, `~matplotlib.ticker.LogLocator` is used instead.
+
 Returns
 -------
 `~.contour.QuadContourSet`