One of the challenges of working in the polar Magnetosphere-Ionosphere-Thermosphere (MIT) system is choosing an appropriate coordinate system. The ocbpy module converts between the Altitude Adjusted Corrected GeoMagnetic (AACGM) coordinates and a grid that is constructed relative to the Open Closed field line Boundary (OCB). This is particulary useful for statistical studies of the poles, where gridding relative to a fixed magnetic coordinate system would cause averaging of different physical regions, such as auroral and polar cap measurements. This coordinate system is described in Chisham (2017).