We present a new method to test the statistical accuracy of field-aligned mappings by using a large magnetospheric data set and apply the method to the Tsyganenko [1989> model. The obtained errors in the field-aligned mappings are generally small in the auroral zone outside the midnight sector but become larger on the nightside and within the polar cap. The model tail field is overstretched near midnight and the model field lines flare out toward the flanks and toward high Z values too much. The results also imply that there is a shear layer between the plasma sheet and lobe that could be indicative of the region 1 field-aligned current system. The large-scale mapping properties suggest that the magnetotail field is asymmetric with respect to the noon-midnight meridian: the model better represents the evening-sector field configuration, whereas the morning-sector model field lines map too far down the tail. ¿ American Geophysical Union 1996