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A kinematic formalism for the Eulerian and Lagrangian analysis of drifter data is developed for homogeneous, isotropic, two-dimensional flows which exhibit a preferred sense of rotation. Principal results include a new measure of rotation h*, defined from orthogonal velocity components, which is related to the covariance of horizontal divergence and rate of change of vorticity. An analogous Lagrangian correlation hL may indicate a rotational sense opposite to h* due to the preferential sampling by drifters of regions of previous net convergence which are regions of cyclonic vorticity for quasi-geostrophic motions. These kinematic results are illustrated by an analysis of 197 iceberg trajectories from the Labrador shelf, which do indeed show opposite rotational senses for h* and hL.