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.