The Antarctic Circle's latitude fluctuates due to tidal forces.
}  For points not on the surface of the ellipsoid, the relationship involves additionally the ellipsoidal height h:                            (                ,        h        )        =                  tan                                  1                                            (                                                                      N                  (                  1                                    f                                      )                                          2                                                        +                  h                                                  N                  +                  h                                                      tan                                            )                      {\displaystyle \theta (\phi ,h)=\tan ^{-1}\left({\frac {N(1-f)^{2}+h}{N+h}}\tan \phi \right)}  The geodetic and geocentric latitudes are equal at the equator and at the poles but at other latitudes they differ by a few minutes of arc
 The name "isometric" arises from the fact that at any point on the ellipsoid equal increments of  and longitude  give rise to equal distance displacements along the meridians and parallels respectively

