tes the image in <code><a href="../Classes/MapCache.html#/s:8MapCacheAAC04diskB0AA04DiskB0Cvp">diskCache</a></code> and returns the received <code>Data</code>  through the  <code>sucess</code> closure.
If something goes wrong it invokes the <code>failure</code>closure  passing the <code>error</code>returned by the system.</p>

                      </div>
                      <div class="declaration">
                        <h4>Declaration</h4>
                        <div class="language">
              