An anatomical mapping system and method includes mapping electrodes configured to detect activation signals of cardiac activity. A processing system is configured to record the detected activation signals and generate a vector field for each sensed activation signal during each instance of the physiological activity. The processing system determines an onset time and alternative onset time candidates, identifies an initial vector field template based on a degree of similarity between the initial vector field and a vector field template from a bank of templates, then determines an optimized onset time for each activation signal based on a degree similarity between the onset time candidates and initial vector field template.