For any Euclidean neighborhood "U", a homeomorphism formula_6 is called a coordinate chart on "U" (although the word "chart" is frequently used to refer to the domain or range of such a map). A space "M" is locally Euclidean if and only if it can be covered by Euclidean neighborhoods. A set of Euclidean neighborhoods that cover "M", together with their coordinate charts, is called an atlas on "M". (The terminology comes from an analogy with cartography whereby a spherical globe can be described by an atlas of flat maps or charts).