I made a map.world file and placed it under

/opt/ros/kinetic/share/turtlebot_gazebo/worlds

and ran

roslaunch turtlebot_gazebo turtlebot_world.launch world_file:=/opt/ros/kinetic/share/turtlebot_gazebo/worlds/map.world 

as mentioned here

I see the map but I don't see turtlebot. What am I doing wrong?