Output from highly resolved, long-duration ocean models, and measurements taken by satellites and other modern observational tools, present critical problems in storage and assessment. While empirical orthogonal function analysis (EOFA) can be useful for data compression, the data are often difficult to assess in compressed form. A relatively new procedure, polytopic vector analysis, has compression capabilities equal to those of EOFA but improves assessment of the data in the compressed form. The two procedures are illustrated by analysis of upper layer quasi-geostrophic potential vorticity from a simple two-layer ocean circulation model. ¿ American Geophysical Union 1992