The concept of Samosaran - just like Tirthankar-nam-karan - is only available in Jainism and not in any other religion.
The creation of samosaran is done by four kinds of Dev (Gods) when a Tirthankar attains Keval Gyan(Complete knowledge). The shape of samosaran is either round or even square. It is of about 8 miles i.e. approx. of 1 yojan. This immensely beautiful development is done so that all and sundry on Earth, sky, water can hear the Tirthankar's speech when they attain keval gyan.