The electron drift velocities in the ionosphere can be measured as a function of both latitude and longitude using coherent radar systems like STARE and SABRE. The temporal resolution of the observations is high compared to the time it takes for the field of view to corotate with the earth over a longitude interval equal to its longitudinal width. An analysis technique is developed that allows us to determine whether an observed time variation is caused by spatial effects or by real time changes. Three events, during which the flow was dominated by spatial variations, have been analyzed and are found to show good agreement with model predictions.