title: geom_sf mapping points/shapes
body: <p>I am using the Tigris package to download shape files with the code, </p>
  
  <pre><code>options(tigris_class = "SF") 
  </code></pre>
  
  <p>While I can easily map polygons</p>
  
  <pre><code>ggplot(data=zctas) +
    geom_sf(aes())
  </code></pre>
  
  <p>I am struggling to create a marker/point instead of a filled polygon (for example, a shape -- like a circle inside a zctas) as the shape file I've pulled down from tigris does not have a lat/long for the x and y AES mapping. The shape file has a "geometry" column, and I am wondering if I can use that? </p>
  
  <p>The documentation here, <a href="https://ggplot2.tidyverse.org/reference/ggsf.html" rel="nofollow noreferrer">https://ggplot2.tidyverse.org/reference/ggsf.html</a></p>
  
  <p>appears to indicate the geom_sf can be used go create points? (I am guessing using the centroid of the zctas' polygon?) but I haven't been able to find an example? 
  Grateful for any resources to identify code that maps points from this Tigris generated shape-file, and or tips and/or alternative approaches.</p>