If it did not do this, the design would look wrong when it’s finished which leads to pull compensation. This step is also when the digitized file explains the order in which each part of the design is to be embroidered, such as filling the design and then the border over the edge. Once this is done, the digitizer thinks of a path for the embroidery to follow which then tells the embroidery machine where to begin and when to end the design.
The backing is a piece of material that is hooped and acts like a stabilizer which stops the fabric from stretching or puckering throughout the embroidery process. Underlay is the stitching in the design that is done first and is used to hold the fabric to the backing.