<p dir="auto">Plot function in matplotlib 3.1.3 generate following strips.</p>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="ones = np.ones((200,100))
cumsum = np.cumsum(ones, axis=1)
plt.plot(cumsum, linestyle='', marker='o', markersize=0.6, color=&quot;k&quot;);"><pre class="notranslate"><code class="notranslate">ones = np.ones((200,100))
cumsum = np.cumsum(ones, axis=1)
plt.plot(cumsum, linestyle='', marker='o', markersize=0.6, color="k");
</code></pre></div>
<p dir="auto"><a target="_blank" rel="noopener noreferrer nofollow" href="https://user-images.githubusercontent.com/38831582/76927446-4d01f580-6922-11ea-9619-077d7ad6a97e.jpg"><img src="https://user-images.githubusercontent.com/38831582/76927446-4d01f580-6922-11ea-9619-077d7ad6a97e.jpg" alt="200" style="max-width: 100%;"></a></p>
<h3 dir="auto">Bug report</h3>
<p dir="auto"><strong>Bug summary</strong></p>
<p dir="auto">When I try to plot a scatterplot where all points are positioned in a regular 2D-grid layout, plotted points are not evenly spaced. Spacings differ systematically which leads to strange regular vertical patterns. With a 100x100 grid, this is the case for (9, 9) or smaller figures. Patterns get less visible with larger figures and disappear around (12, 12)</p>
<p dir="auto"><strong>Code for reproduction</strong></p>

<div class="highlight highlight-source-python notranslate position-relative overflow-auto" dir="auto" data-snippet-clipboard-copy-content="import numpy as np
import matplotlib.pyplot as plt

x = np.tile(np.arange(100), 100)
y = np.repeat(np.arange(100), 100)

f, ax = plt.subplots(figsize=(7, 7))
ax.scatter(x, y, s=1, c='k')"><pre class="notranslate"><span class="pl-k">import</span> <span class="pl-s1">numpy</span> <span class="pl-k">as</span> <span class="pl-s1">np</span>
<span class="pl-k">import</span> <span class="pl-s1">matplotlib</span>.<span class="pl-s1">pyplot</span> <span class="pl-k">as</span> <span class="pl-s1">plt</span>

<span class="pl-s1">x</span> <span class="pl-c1">=</span> <span class="pl-s1">np</span>.<span class="pl-en">tile</span>(<span class="pl-s1">np</span>.<span class="pl-en">arange</span>(<span class="pl-c1">100</span>), <span class="pl-c1">100</span>)
<span class="pl-s1">y</span> <span class="pl-c1">=</span> <span class="pl-s1">np</span>.<span class="pl-en">repeat</span>(<span class="pl-s1">np</span>.<span class="pl-en">arange</span>(<span class="pl-c1">100</span>), <span class="pl-c1">100</span>)

<span class="pl-s1">f</span>, <span class="pl-s1">ax</span> <span class="pl-c1">=</span> <span class="pl-s1">plt</span>.<span class="pl-en">subplots</span>(<span class="pl-s1">figsize</span><span class="pl-c1">=</span>(<span class="pl-c1">7</span>, <span class="pl-c1">7</span>))
<span class="pl-s1">ax</span>.<span class="pl-en">scatter</span>(<span class="pl-s1">x</span>, <span class="pl-s1">y</span>, <span class="pl-s1">s</span><span class="pl-c1">=</span><span class="pl-c1">1</span>, <span class="pl-s1">c</span><span class="pl-c1">=</span><span class="pl-s">'k'</span>)</pre></div>
<p dir="auto"><strong>Actual outcome</strong></p>
<p dir="auto"><a target="_blank" rel="noopener noreferrer nofollow" href="https://user-images.githubusercontent.com/1140359/50409159-5ef7f580-07be-11e9-9083-5ce18d34311a.png"><img src="https://user-images.githubusercontent.com/1140359/50409159-5ef7f580-07be-11e9-9083-5ce18d34311a.png" alt="image" style="max-width: 100%;"></a></p>
<p dir="auto"><strong>Expected outcome</strong></p>
<p dir="auto">Here is a figure of size (12, 12):</p>
<p dir="auto"><a target="_blank" rel="noopener noreferrer nofollow" href="https://user-images.githubusercontent.com/1140359/50409217-fa896600-07be-11e9-8ce9-24a8294472cd.png"><img src="https://user-images.githubusercontent.com/1140359/50409217-fa896600-07be-11e9-8ce9-24a8294472cd.png" alt="image" style="max-width: 100%;"></a></p>
<p dir="auto">Here is a figure from R for comparison:</p>
<p dir="auto"><a target="_blank" rel="noopener noreferrer nofollow" href="https://user-images.githubusercontent.com/1140359/50409242-3de3d480-07bf-11e9-99f1-35cc481e0edf.png"><img src="https://user-images.githubusercontent.com/1140359/50409242-3de3d480-07bf-11e9-99f1-35cc481e0edf.png" alt="image" style="max-width: 100%;"></a></p>
<p dir="auto"><strong>Matplotlib version</strong></p>

<ul dir="auto">
<li>Operating system: osx 10.14</li>
<li>Matplotlib version: 3.0.2</li>
<li>Matplotlib backend (<code class="notranslate">print(matplotlib.get_backend())</code>): module://ipykernel.pylab.backend_inline</li>
<li>Python version: 3.6.6</li>
<li>Jupyter version (if applicable): 4.4.0</li>
</ul>