Bivariate histogram for visualizing the structure in datasets with large numbers.
Hexagon binning is a form of bivariate histogram useful for visualizing the structure in datasets with large numbers, particularly when many similar values cause overplotting.
A grid of interlocking hexagons is laid on a field of 2-dimensional data and for each hexagon the point counts are determined. Originally an enhancement to the visualize traditional XY scatterplot hexagon binning has been used increasingly in cartography as well.
D. B. Carr, R. J. Littlefield, W. L. Nicholson and J. S. Littlefield: Scatterplot Matrix Techniques for Large N. Journal of the American Statistical Association, Vol. 82, No. 398 (Jun., 1987), pp. 424-4364
Nicholas Lewin-Koh (2011): Hexagon Binning: an Overview
Zachary Forest Johnson (2011): Hexbins!