1. A method for mapping an anatomical structure, the method comprising: sensing activation signals during an instance of physiological activity with a plurality of mapping electrodes disposed in or near the anatomical structure; generating a vector field for each sensed activation signal during each instance of the physiological activity; determining an onset time and alternative onset time candidates for each activation signal; identifying a vector field pattern template for each activation signal based on a degree of similarity between the generated vector field and at least one vector field template pattern; determining an optimized onset time for each activation signal based on the corresponding onset time candidates and the vector field pattern template; generating an updated vector field for each sensed activation signal based on the optimized onset time for each activation signal; and updating the identified vector field pattern template based on the sensed activation signals.