title: Error installing ros map_server
body: <p>When I try to install map_server on ROS, it occurred errors like the following:</p>
  
  <pre><code>Reading package lists... Done
  Building dependency tree       
  Reading state information... Done
  Some packages could not be installed. This may mean that you have
  requested an impossible situation or if you are using the unstable
  distribution that some required packages have not yet been created
  or been moved out of Incoming.
  The following information may help to resolve the situation:
  
  The following packages have unmet dependencies:
   ros-hydro-map-server : Depends: ros-hydro-roscpp but it is not going to be installed
                          Depends: ros-hydro-rostest but it is not going to be installed
                          Depends: ros-hydro-tf but it is not going to be installed
  E: Unable to correct problems, you have held broken packages.
  </code></pre>
  
  <p>How am I supposed to solve it?</p>