title: How can I partially plot a Healpix map using Healpy?
body: <p>When working with healpy, I am able to plot a Healpix map in Mollview using </p>
  
  <pre><code>import healpy
  map = 'filename.fits'
  healpy.visufunc.mollview(map)
  </code></pre>
  
  <p>or as in the tutorial</p>
  
  <pre><code>&gt;&gt;&gt; import numpy as np
  &gt;&gt;&gt; import healpy as hp
  &gt;&gt;&gt; NSIDE = 32
  &gt;&gt;&gt; m = np.arange(hp.nside2npix(NSIDE))
  &gt;&gt;&gt; hp.mollview(m, title="Mollview image RING")
  </code></pre>
  
  <p>which outputs </p>
  
  <p><a href="https://i.stack.imgur.com/OgW2o.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/OgW2o.png" alt="enter image description here"></a></p>
  
  <p>Is there a way to display only certain regions of the map? For example, only the upper hemisphere, or only the left side? </p>
  
  <p>What I have in mind is viewing only small patches of the sky to see small point sources, or something like the "half-sky" projection from LSST</p>
  
  <p><a href="https://i.stack.imgur.com/CSZC0.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/CSZC0.png" alt="enter image description here"></a></p>