What shape of placemat should go on a round table?

For a round table, I prefer a round placemat. I have owned both rectangular and round kitchen tables and I have always used placemats on them. They are just easier to keep clean than a tablecloth. Although I have to admit, that I mostly use the placemats that I buy more for decoration than practicality! I really like these: http://www.pacificmerchants.com/table-placemats/table-placemats-round.html