Download an outline of a world map from your computer. It should be 8" by 11 1/2". You can find outlines of world maps from various educational sites.
Make a copy of the world map on a transparency. Make sure that you have the kind of transparency that will run through a copy machine.
Hang the paper that you are going to use to make your world map on the wall. Tape down the edges so that the paper doesn't shift. Also, make sure that the wall is a smooth surface.
Put your transparency of the world map outline on an overhead projector. Point the projector at the paper you have hung on the wall. Adjust the settings so that the outline of the world map is clear and so it is the size that you want. With an overhead projector, you can create just about any size of world map--even a wall world map!
Secure the transparency to the projector so that it does not shift. Using a pencil, draw an the outline of the world map on the paper that you hung on the wall.
When you are finished drawing the outline of the world map, color and label the countries. If you have made a very large map, you may wish to paint the countries.