Definition:Atlas

Definition
Let $M$ be a locally Euclidean space of dimension $d$.

Then an atlas of class $C^k$ on $M$ is a collection of co-ordinate systems $\mathscr F = \{(U_\alpha,\phi_\alpha) : \alpha \in A\}$ indexed by some set $A$ such that:


 * $(1): \quad \displaystyle \bigcup_{\alpha \mathop \in A} U_\alpha = M$


 * $(2): \quad \phi_\alpha \circ \phi_\beta^{-1}$ is of class $C^k$ as a map $\phi_\beta\left(U_\alpha \cap U_\beta\right) \to \phi_\alpha\left(U_\alpha \cap U_\beta\right)$ for all $\alpha,\beta \in A$

Also known as
Some sources refer to an atlas as a pre-differentiable structure.