## As graph matrices?

I would like to please guide me on this question:
Let $\displaystyle$S_+$$denote the set of semi positive definite matrices in \displaystyle \mathbb{R}^{2\times 2}$$ is known that $\displaystyle$S_+\subseteq Sym \simeq\mathbb{R}^{3}$$,wherein \displaystyle Sym$$ are the matrices symmetric. But Is it possible to give a geometric interpretation of $\displaystyle$S_+$$in \displaystyle \mathbb{R}^{3}$$? Can be graphed?
Thank you very much for your attention, any suggestions are welcome.