Why dosa is always round?????

Because,it is easy to get that shape.If you like to get in other polygon shapes,just cut those unwanted portions.That's simple as that.We can add on,why chapathies and pooris are round,also.Cheers!

Who said ? I ate a Diamond Shaped Dosa, day before yesterday in a restaurant near to my office. Though it costed me more than the regular dosa, I was happy that I can eat something different.

It's because it is easiest to make that way. There is no reason why you shouldn't make it another way (in a square or triangle) but it would probably need a different shaped pan. Generally Dosa is prepared from a batter prepared from a ground mixture. This batter is then spread from the centre to the sides in a circular motion on a hot tava(flat circular frying pan). When the batter is prepared from powdered ingredients, it is poured in a circular motion in such a way that the sides are formed first and then the center is filled with batter.