hey guys, I've been trying

roslaunch turtlebot_gazebo turtlebot_world.launch world_file:=worlds/willowgarage.world

but it's not loading the willowgarage world, what I see is a blank gazebo world, So i wanted to know how could I get the willowgarage world or some similar world to execute SLAM on, how could I install similar packages in ros, or how could I develop my own world similar to willowgarage.

Further I am using turtlebot_gazebo package, gmapping_demo and amcl_demo to execute slam Please help me guys, it would be very helpful.