roslaunch and map_server

edit

Hello,

you can try the following:

<launch>

  <arg name="map_file" default="$(find [package where your yaml file is])/mymap.yaml"/>

  <!-- Run the map server -->
  <node name="map_server" pkg="map_server" type="map_server" args="$(arg map_file)" />

</launch>

I would strongly advise you to have a look at this tutorial that explains how to setup the navigation stack for a robot.

Also have a look at the xml tags allowed in launch files here.

Raph