title: ImportError: Spatial indexes require either `rtree` or `pygeos` in geopanda but rtree is installed
body: <p>I am trying to clip spatial data in python but when I run my code...</p>
  <pre><code>europe = gpd.clip(worldmap, europe_bound_gdf)
  </code></pre>
  <p>... I get the error:</p>
  <p>(<code>ImportError: Spatial indexes require either </code>rtree<code>or</code>pygeos`.)</p>
  <p>When I try to install rtree using:</p>
  <pre><code>pip3 install rtree
  </code></pre>
  <p>I'm told:</p>
  <pre><code>Requirement already satisfied: rtree in /Users/joshuajones/.pyenv/versions/3.9.4/lib/python3.9/site-packages (0.9.7`)
  </code></pre>
  <p>So why is my code not working?</p>