Similitude is a way of making models that look like something else. It involves taking measurements of the real object you are trying to make a model of, and then creating a model that is exactly the same shape and size, but smaller. For example, if you were making a model of a ship, you would measure the length, width, and height of the real ship, and then make a smaller model that is the exact same proportions. This allows the model to look just like the real ship, only in miniature.