Tag Clustering:

(a) Crowd generated tags (grey) within a 2 dimensional space (white) on a 5×5 grid; (b) Kernel density visualized through a color gradient where high density is represented as red and low density as blue; (c)Tag clusters are annotated with semitransparent circles of variable radii, determined as a dependent function of the normalized kernel density estimate of a cluster's center. Large radius circles represent a location of high agreement across the all participants. Satellite imagery provided courtesy of the GeoEye Foundation.