A set is called a regular surface if each of its points has a neighborhood in that is diffeomorphic to an open set in . That is, for every , there exists a neighborhood, , of in , an open set , and a diffeomorphism . Such a diffeomorphism is called a surface patch or a coordinate chart. A collection of surface patches that together cover all of the points of is called an atlas for .
使用する際の注意点
Some authors refer to the pair of the neighborhood the mapping is defined on and the mapping together (i.e. instead of , where ) as the coordinate chart while referring to the mapping alone as the coordinate map.