Births: a heat map

This is a heat map showing what is the most common day of birth in U.S. My original intent was collecting data for several countries and comparing them, but retrieving data with the day and the month of the birth proved exceptionally hard. When I get them I update this chart.

A heat map is a graphical representation of a data matrix, where each individual value is coded by a difference in colors (hue or saturation, here I'm using a sequential Brewer palette for the colours.). The legend below the heat map indicates the range of values for each color. Hover over each day to see more information.

The data includes US births from 1/1/1969 to 31/12/1988. Source of the data: Chris Mulligan. Inspired by Tom May.