Mathias has worked extensively on topical photographic essays in locations such as Afghanistan, Australia, Bangladesh, Burma, Cambodia, East Timor, India, Indonesia, Iraq, Japan, Jordan, Kiribati, Mozambique, Nepal, Pakistan, Papua New Guinea, South Africa, Thailand, United Kingdom and Zimbabwe. In 2002, Mathias published his first book, sponsored by Leica, Viva Timor Loro S’ae, Long Live East Timor 1999 – 2002 which was launched in Australia and East Timor.