A topper that covers the top of the head (customer has his own hair on the back and sides) is by far the most common type of hair piece. But many customers have different forms of hair loss. Here's a photo of a customer that has lost hair only on the front top section. He still has hair on the top and in the back plus his sides and back. This is a partial template. And it has many variations including people that just want to bring the hair line forward and fill in temple recession.
Regards,
John