How can agnosticism and atheism be of the same category? Agnosticism should only be applied to atheism IF they house some uncertainty towards their view. This goes for theism, too. In short, agnosticism can describe both theists and atheists who feel that they haven't got the means to prove their claims that the metaphysical can or can not exist. (Just did some quick research.)
I'm an agnostic theist, btw.