Projection map from projective space is not well defined?

Question

Let $f: \mathbb{P^2} \to \mathbb{P^1}$ send $(x,y,z)$ to $(x,z)$. My book is telling me that this map is not well defined at $(0,0,1)$. How is this the case? Here $\mathbb{P}^1$ and $\mathbb{P}^2$ are the projective spaces over $\mathbb{C}$, that is $\mathbb{P^n}$ is the quotient of $\mathbb{C}^{n+1} - 0$ over $\mathbb{C}^{\times}$.