title: How to convert NAD 83 coordinates to latitude and longitude with rgdal package?
body: <p>I have coordinates, all of which should be located in DC, but I cannot figure out how to convert them from NAD 83 to latitude and longitude in R. I'm using the <code>spTransform()</code> function in the rgdal package and get an error about non-conformant data.</p>
  
  <pre><code>library(rgdal)
  nad83_coords &lt;- data.frame(x=c(396842.6, 397886.9, 398315.5, 398154.3, 398010.3), y=c(140887.1, 139847.0, 138743.9, 139534.5, 138697.3))
  coordinates(nad83_coords) &lt;- c('x', 'y')
  proj4string(nad83_coords) &lt;- CRS("+init=epsg:4269")
  Error in `proj4string&lt;-`(`*tmp*`, value = &lt;S4 object of class "CRS"&gt;) : 
    Geographical CRS given to non-conformant data: 398315.5 140887.1
  </code></pre>
  
  <p>Other combinations of proj4strings yield the same error. I believe the error is because the coordinates are too large, but I'm not sure why that would be. The documentation for the coordinates is below:</p>
  
  <blockquote>
    <p>Values are in the Maryland State Plane meters NAD 83 map projection.</p>
  </blockquote>
  
  <p>I'm very new to mapping and projections, and any help is appreciated.</p>