title: Create regional lat, long dataframe from group of states
body: <p>I have been using <code>urbnmapr</code> for all of my mapmaking and it contains nice borders for mapping US states. I now need the outer border of a few states to make a regional map and am looking for a way to filter the dataframe to include only the outer borders.</p>
  <p>I will use this outer border to mask a raster image. The region I am working with is</p>
  <pre><code>filter(urbnmapr::states, state_name %in% c(&quot;South Dakota&quot;, &quot;Nebraska&quot;, &quot;Iowa&quot;, &quot;Minnesota&quot;,
                                                &quot;Missouri&quot;, &quot;Michigan&quot;, &quot;Indiana&quot;, &quot;Illinois&quot;,
                                                &quot;Wisconsin&quot;, &quot;Kansas&quot;, &quot;Ohio&quot;, &quot;North Dakota&quot;))
  </code></pre>
  <p>Open to any ideas that will give me an object I can use to mask a raster of this region.</p>