Technical help questions, such as this, should be asked on answers.gazebosim.org. This forum is designed for general discussions, community organization, news, and other topics.
The reason for the separation is to provide distinct places where people can either seek help to their simulation needs (answers.gazebosim.org) or discuss ideas, sync up with other users, read news, etc (community.gazebosim.org).
In response to your question, I believe you are asking if Gazebo requires a map of the world in order to simulate obstacles. The short answer is yes. However, Gazebo can’t take a 2D map and construct 3D obstacles. You’ll have to construct a world that matches your map. A good place to learn more are these tutorials.