title: Labeling polygons with geom_sf, ggplot
body: <p>I am attempting to label polygons from a spatial feature data frame using ggplot2. I am trying to replicate the description <a href="https://ryanpeek.github.io/2017-11-05-mapping-with-sf-Part-2/" rel="nofollow noreferrer">here</a> under the heading, "Download Some Boundary Data: State/County/HUC"</p>
  
  <p>This is my code to try to get the lat and lon values to use for the label location in geom_text():</p>
  
  <pre><code>selected_sites &lt;- arc.open(survey_sites)
  ss &lt;- arc.select(selected_sites)
  ss_shape &lt;- arc.data2sf(ss)
  refcode_list &lt;- ss$refcode
  
  ss_shape &lt;- ss_shape %&gt;%
    mutate(lon=map(geometry, ~st_centroid(.x)[[1]]),
           lat=map(geometry, ~st_centroid(.x)[[2]]))
  </code></pre>
  
  <p>I keep getting the following error:</p>
  
  <blockquote>
    <p>Error in mutate_impl(.data, dots) :<br>
          Evaluation error: <code>.x</code> is not a vector (closure).</p>
  </blockquote>