If you haven’t yet checked out The Data Viz Challenge, you should. A data visualization contest? Sponsored by Google and Eyebeam? Focusing on the federal budget?! There is basically nothing in the world more up our alley. Yes. A thousand times yes.

And yet I do feel obliged to offer one small criticism: I think the contest would be a little more exciting if entries weren’t limited to using data from What We Pay For. Mind you, this is not because of anything wrong with WWPF. That site has done a very nice job of parsing budget data and, through the Challenge’s website, exposing it via an API.

The problem is that the budget is only part of the story. As Kaitlin has already explained in this space, tax expenditures—more commonly known as tax breaks—are vital to understanding our nation’s finances. When the government declines to collect tax revenue from some particular individual or industry, it’s not very different from simply sending them a check. The beneficiary has more money and, all else being equal, the rest of us have to pay more taxes (or take on more debt) to make up for it.

Unfortunately, this is the point at which politics enters the equation. The two major parties tend to pursue their spending priorities in different ways, and this has created political incentives for pretending that tax expenditures don’t affect the budget. But this is silly—it’s like pretending that if you worked two jobs and neglected to deposit your paycheck from one of them it would have no effect on your finances.

You can find people from both sides of the aisle saying unsupportable things about tax expenditures, but the truth is that every serious scholar who works on this issue regards tax expenditures as a type of spending. That’s why the literature uses the word “expenditure.”

I don’t know if WWPF declined to wade into this space because it’s politically charged or because the data’s historically been so tough to access, but I wish they had decided differently. If you don’t include tax expenditures, you wind up ignoring huge government subsidies to business (accelerated depreciation), housing (mortgage interest tax deduction) and every kind of nonprofit, from museums to soup kitchens to the NCAA (tax exemption). This isn’t to say that we shouldn’t subsidize those entities and uses. Maybe we should! But we should at least talk about it. We need to make sure these expenditures are considered if we’re going to get a clear understanding of our nation’s finances. Make no mistake, we’re talking about a lot of money — have a look at the chart from Kaitlin’s post and you’ll see what I mean.

At any rate, I’m sure that we’ll see some stunning visualizations come out of this contest, and I don’t hesitate to encourage anyone reading this to participate. But now that Sunlight and the Pew Charitable Trusts have worked together to expose data on tax expenditures—and we’ll be adding more such data soon—I hope the visualization community will be inspired to tell that part of the tale as well. Without it, any story about our government’s spending is incomplete.