This is the first stage of putting a mural onto a wall - you blow up your sketch by means of a projector and begin the process of drawing it onto the wall. This can take a long time as you want to make sure it is laid on the area precisely. Another aspect about doing this is to make sure someone doesn't bump the projector or jostle the floor so that the image moves even a little bit. Once I had this happen simply by people walking on the hard court floor, to try and realign it was a nightmare. I now ask that the gym be completely empty when I do this - I have a fear of some student shooting a b-ball and knocking the projector to the ground from a missed shot. Projectors are pricey.