title: Converting area within a polygon of coordinates to metres
body: <p>given a set of coordinates</p>
  
  <pre><code> lat &lt;- c(47.2325618, 47.2328269, 47.2330041, 47.2330481, 47.2330914, 
            47.2331172, 47.2331291, 47.2331499)
   lon &lt;- c(11.3707441, 11.3707791, 11.3708087, 11.3708031, 11.3707818, 
            11.3707337, 11.3706588, 11.370284)
  coords &lt;- cbind(lon,lat)
  </code></pre>
  
  <p>I want to calculate the area of the polygon. I use the function <code>areapl()</code> from package <em>splancs</em>:</p>
  
  <pre><code>library(splancs)
  areapl(coords)
  # [1] 1.4768e-07
  </code></pre>
  
  <p>this leaves me with a dimension in degrees squared (?). so my question is: <strong>how do i convert this into metres/kilometres?</strong></p>
  
  <p>thanks a lot in advance.</p>