In about three months, the federal government will begin gathering data for the census, the enormously complicated national survey required every 10 years by Article 1 of the U.S. Constitution.

It’s a daunting task to count every person living in a nation as large as ours, and after months of roiling controversies over the inclusion of a question about citizenship, foot-dragging by congressional budgeters and the cancellation of crucial field tests, it can only be hoped that the Census Bureau will get the count right. In fact, it must, because an awful lot is riding on it.

The census serves two primary purposes. First, it is used to determine how many seats in Congress each state will have, and to establish boundary lines for congressional and, often, state legislative districts based on population. The number of congressional seats allotted to each state also helps determine how many electoral college votes the state has in presidential elections.

Second, the federal government uses census data to determine the allocation of federal aid. Nearly $900 billion nationwide is disbursed on the basis of census data.

So census miscounts can have profound effects. And in recent censuses, urban centers where minorities and immigrants tended to cluster have been undercounted. In fact, a census review of its 2010 count estimated that it missed more than 2 percent of the nation’s black population and 1.5 percent of the Latino population, with disconcertingly higher misses in narrower categories. For instance, it missed about 10 percent of black males ages 30 to 46, and 5.9 percent in their late teens and 20s. It also missed about 5 percent of Latino males. The 2010 census had trouble counting children too, missing an estimated 1 million kids under age 5, according to another review by the Census Bureau.

At the same time the census tended to overcount white populations, which means that redistricting after the 2010 census shifted some political weight from urban centers, which tend to vote for Democrats, to suburban and rural populations, which tend to vote for Republicans.

These undercounts and overcounts disproportionately shortchange minority, immigrant and low-income communities.

There are technical uncertainties about the census, too.

For the first time, the 2020 census will be conducted mostly online using a system that has only been lightly tested in the field because of budget restraints.

While some experts believe the Census Bureau will be ready, and the Government Accounting Office says the bureau addressed many concerns the GAO had raised and that preparations now “are generally on track,” advocates for communities with histories of being undercounted remain skeptical.

Part of the problem, critics say, is that the Census Bureau was slow in working with states and local stakeholders on public awareness campaigns; the delay, they fear, will make it harder to reach members of historically undercounted communities.

To ensure a more accurate count, many states have crafted their own outreach and public information campaigns.

California will spend $187 million, by far the most of about two dozen states that will spend more than $300 million combined.

While it seems odd to spend state money to help ensure an accurate federal census, the stakes are sufficiently high for California to justify the expense.

A reliable census is fundamental to America’s representative democracy, and we must ensure that the 2020 count is conducted under the highest possible professional standards.