1. A method for displaying a density surface on a map, the method comprising: maintaining data that represents an association between a value and a first geographic coordinate; dividing a map plane into a plurality of cells; identifying a first cell of said plurality of cells based at least in part on said first geographic coordinate; for at least one cell of said plurality of cells in proximity to said first cell, determining a first planar coordinate in said map plane that corresponds to the at least one cell, transforming said first planar coordinate into a second geographic coordinate, computing a geodetic distance between said second geographic coordinate and a geographic coordinate corresponding to said first cell, determining a density value to be allocated to the at least one cell based at least in part on said geodetic distance, and allocating the density value to the at least one cell; causing a density surface to be displayed on a map based at least in part on the density value allocated to the at least one cell; and wherein the method is performed by one or more computing devices.