In the theory of Lorentzian manifolds, spherically symmetric spacetimes admit a family of nested round spheres.
There are several different types of coordinate chart that are adapted to this family of nested spheres, each introducing a different kind of distortion.
Another popular choice is the isotropic chart, which correctly represents angles (but in general distorts both radial and transverse distances).
There are other possible charts; the article on spherically symmetric spacetime describes a coordinate system with intuitively appealing features for studying infalling matter.
In a Gaussian polar chart (on a static spherically symmetric spacetime), the metric (aka line element) takes the form Depending on context, it may be appropriate to regard