The ionosphere provides a large and variable fraction of the plasma that makes up the Earth's magnetosphere. The sparseness of ion outflow observations and limitations of global magnetospheric models have limited progress in understanding how spatial and temporal variations in the ionospheric component of the magnetosphere affects magnetospheric processes such as storms and substorms. Moreover, because existing comprehensive ion outflow data sets are not organized in terms of large-scale, dynamic, magnetospheric features, they cannot be used as boundary conditions or ground truth for large-scale magnetospheric models. This paper presents a method to self-consistently generate dynamic auroral zone boundaries from ion and electron data obtained on the same platform with mass-resolved ion outflow observations. We show that this dynamic coordinate system can be used to organize the ion outflow observations so that they are compatible to use with large-scale magnetospheric models.