In a method for clustering position determination for providing position determination assisting data in a cellular communications network, detecting S1 an event, such as the occurrence of an emergency call or sudden drop in radio quality, providing a tag S2 for the detected event comprising event specific information. Subsequently, providing S3 high precision position measurements the said tagged detected event, and repeating S4 said detecting and providing steps a plurality of times. Finally, obtaining local clusters S5 of high-precision position measurements based on the event specific tag.