"""
US Population: Wrapped Facet
============================
This chart visualizes the age distribution of the US population over time,
using a wrapped faceting of the data by decade.
"""
# category: case studies
import altair as alt
from vega_datasets import data

source = data.population.url

alt.Chart(source).mark_area().encode(
    x='age:O',
    y=alt.Y('sum(people):Q').title('Population').axis(format='~s'),
    facet=alt.Facet('year:O').columns(5),
).properties(
    title='US Age Distribution By Year',
    width=90,
    height=80
)
