In a method of improved clustering for providing position determination assisting data in a cellular communication system, providing (S10) a plurality of clusters of points, said points being results of high-precision reference measurements, said points of each of said cluster having the same unique radio fingerprinting tag, identifying (S20) a target cluster, said target cluster having a number of points less than a predetermined threshold. Finally, merging (S30) said target cluster with at least one adjacent cluster of said provided plurality of clusters to provide a merged cluster with an increased number of high-precision reference measurements.