matplotlib · timhoffm · Jul 4, 2018 · Nov 16, 2017
diff --git a/doc/api/next_api_changes/2018-07-02-JMK.rst b/doc/api/next_api_changes/2018-07-02-JMK.rst
@@ -0,0 +1,37 @@
+Changed default `AutoDateLocator` kwarg ``interval_multiples`` to ``True``
+--------------------------------------------------------------------------
+
+The default value of the tick locator for dates, `.dates.AutoDateLocator`
+kwarg ``interval_multiples`` was set to ``False`` which leads to not-nice
+looking automatic ticks in many instances.  The much nicer
+``interval_multiples=True`` is the new default.  See below to get the
+old behavior back:
+
+  .. plot::
+
+    import matplotlib.pyplot as plt
+    import datetime
+    import matplotlib.dates as mdates
+
+    t0 = datetime.datetime(2009, 8, 20, 1, 10, 12)
+    tf = datetime.datetime(2009, 8, 20, 1, 42, 11)
+
+
+    fig, axs = plt.subplots(1, 2, constrained_layout=True)
+    ax = axs[0]
+    ax.axhspan(t0, tf, facecolor="blue", alpha=0.25)
+    ax.set_ylim(t0 - datetime.timedelta(minutes=3),
+                tf + datetime.timedelta(minutes=3))
+    ax.set_title('NEW DEFAULT')
+
+    ax = axs[1]
+    ax.axhspan(t0, tf, facecolor="blue", alpha=0.25)
+    ax.set_ylim(t0 - datetime.timedelta(minutes=3),
+                tf + datetime.timedelta(minutes=3))
+    # old behavior
+    locator = mdates.AutoDateLocator(interval_multiples=False, )
+    ax.yaxis.set_major_locator(locator)
+    ax.yaxis.set_major_formatter(mdates.AutoDateFormatter(locator))
+
+    ax.set_title('OLD')
+    plt.show()
diff --git a/lib/matplotlib/dates.py b/lib/matplotlib/dates.py
@@ -1158,7 +1158,7 @@ class AutoDateLocator(DateLocator):
     locations.
     """
     def __init__(self, tz=None, minticks=5, maxticks=None,
-                 interval_multiples=False):
+                 interval_multiples=True):
         """
         *minticks* is the minimum number of ticks desired, which is used to
         select the type of ticking (yearly, monthly, etc.).
@@ -1234,6 +1234,12 @@ def __init__(self, tz=None, minticks=5, maxticks=None,
             MICROSECONDLY: [1, 2, 5, 10, 20, 50, 100, 200, 500, 1000, 2000,
                             5000, 10000, 20000, 50000, 100000, 200000, 500000,
                             1000000]}
+        if interval_multiples:
+            # Swap "3" for "4" in the DAILY list; If we use 3 we get bad
+            # tick loc for months w/ 31 days: 1, 4,..., 28, 31, 1
+            # If we use 4 then we get: 1, 5, ... 25, 29, 1
+            self.intervald[DAILY] = [1, 2, 4, 7, 14, 21]
+
         self._byranges = [None, range(1, 13), range(1, 32),
                           range(0, 24), range(0, 60), range(0, 60), None]
 
@@ -1338,7 +1344,11 @@ def get_locator(self, dmin, dmax):
             self._freq = freq
 
             if self._byranges[i] and self.interval_multiples:
-                byranges[i] = self._byranges[i][::interval]
+                if i == DAILY and interval == 14:
+                    # just make first and 15th.  Avoids 30th.
+                    byranges[i] = [1, 15]
+                else:
+                    byranges[i] = self._byranges[i][::interval]
                 interval = 1
             else:
                 byranges[i] = self._byranges[i]

diff --git a/lib/matplotlib/tests/baseline_images/test_axes/pcolor_datetime_axis.png b/lib/matplotlib/tests/baseline_images/test_axes/pcolor_datetime_axis.png
diff --git a/lib/matplotlib/tests/baseline_images/test_axes/pcolormesh_datetime_axis.png b/lib/matplotlib/tests/baseline_images/test_axes/pcolormesh_datetime_axis.png
diff --git a/lib/matplotlib/tests/baseline_images/test_axes/single_date.pdf b/lib/matplotlib/tests/baseline_images/test_axes/single_date.pdf
diff --git a/lib/matplotlib/tests/baseline_images/test_axes/single_date.png b/lib/matplotlib/tests/baseline_images/test_axes/single_date.png