Setting environment variable 'TURTLEBOT_STAGE_MAP_FILE'

I'm trying to get the turtlebot stage simulator running from these instructions: http://wiki.ros.org/turtlebot_stage/Tutorials/indigo/Bring%20up%20TurtleBot%20in%20stage But, putting the first line in the terminal: roslaunch turtlebot_stage turtlebot_in_stage.launch gives this output: ... logging to /home/yaseen-14/.ros/log/0b120c28-319b-11e5-ac3b-685d4316eccf/roslaunch-yaseen14-HP-Pavilion-m6-Notebook-PC-11910.log Checking log directory for disk usage. This may take awhile. Press Ctrl-C to interrupt Done checking log file disk usage. Usage is <1GB. Invalid tag: environment variable 'TURTLEBOT_STAGE_MAP_FILE' is not set. Arg xml is The traceback for the exception was written to the log file Not sure why this is happening but would appreciate if anyone could help me out. Cheers!