title: Extract shapefile value to point with R
body: <p>I want to extract a shapefile value at a particular location. The shapefile I am using is can be found <a href="http://www.marineregions.org/sources.php#iho" rel="nofollow">here</a>, downloaded by clicking <code>Download IHO Sea Areas</code>. The shape file contains all the possible seas.</p>
  
  <p>I can read it and plot it using:</p>
  
  <pre><code>require("maptools")
  require(rgdal)
  require(sp)
  
  ogrListLayers("World_Seas.shp")
  shape &lt;- readOGR("World_Seas.shp", layer="World_Seas") 
  </code></pre>
  
  <p>However, I would like to extract the sea value for a particular location, say</p>
  
  <pre><code>p &lt;- c(-20, 40)
  </code></pre>