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This stacked bar chart is constructed from a CSV file storing the populations of different states by age group. The chart employs conventional margins and a number of D3 features:

• d3.csv - load and parse data
• d3.scale.ordinal - x-position encoding and color encoding
• d3.scale.linear - y-position encoding
• d3.format - SI prefix formatting (e.g., “10M” for 10,000,000)
• d3.max - compute domains
• d3.keys - compute column names
• d3.svg.axis - display axes

This example doesn’t use d3.layout.stack because it’s easy to just stack each state independently via array.forEach. Here, it makes sense to group the rects by state (column), rather than grouping by age group (series), as you do with a stacked area chart.