A system and method are provided for developing a database of body surface ECG P-wave maps for classification and localization of left-sided atrial arrhythmias. The system and method include generating and receiving P-wave data in a subject by left atrial pacing or receiving P-wave data in a subject during spontaneously occurring or induced left atrial arrhythmias; computing (e.g. potential or integral) maps of the P-wave data; classifying the maps specific to a left atrial ectopic origin; verifying the classification procedure; averaging the classified maps into mean maps; and storing and accessing the mean maps in the database. The mean maps of the P-wave data in the database can be used to automatically classify and localize P-wave data from a patient obtained during a left atrial arrhythmia such as atrial tachycardia, focal atrial fibrillation, or orthodromic atrioventricular reentrant tachycardia.