One thing I like is that it's so simple. There's a scatter plot of Australian electorates. One axis is how they voted in the same-sex marriage plebiscite, and you choose the other: average income, percentage over 60 years old, how many speak a language other than English, etc.
As you flick through the options, you get one amorphous blob after another. Then you choose "percentage of atheists", and you see the kind of straight line that usually comes from a physics experiment.
For example, selecting "Secular/No Religion" I see that Sydney scored about 83 on "Yes vote for SSM" (meaning 83% of those voting in Sydney voted in favor, right?). It scored about 44 on "Selected indicator" (in this case "secular", right?).
So -- 44% of Sydney self-reports as "Secular" -- right?