gth)
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      areal (e.g. polygon)
                    </p>
                  </td>
<td>
                    <p>
                      Calculates centroid
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      Empty (e.g. polygon without points)
                    </p>
                  </td>
<td>
                    <p>
                      Throws a