OTTAWA — The census can look dull or irrelevant to the average citizen, a twice-a-decade event that only policy wonks, academics and journalists really care about.

But like the foundation of a building, census data are largely invisible but crucially important, affecting the lives of any citizen who has a child, drives a car, goes to school, moves here from another country, retires, works -- or loses their job -- shops, gets sick, wants to live in a safe neighbourhood, needs help from a charity or wants to know the money they donate will be put to good use.

"It really does touch your life, but not until you need it or you see it do you realize it," says Doug Norris, director general of social and demographic statistics at Statistics Canada until 2005 and now chief demographer and senior vice-president with Environics Analytics.

Since the Conservatives announced three weeks ago they're scrapping Canada's long-form census in 2011 and replacing it with a voluntary survey -- a move they say was prompted by privacy complaints -- opposition has been mounting steadily. The short-form census remains mandatory. An array of experts and organizations has panned the decision, insisting it will destroy the statistical backbone of municipalities, social programs, community organizations and private businesses that touch nearly every aspect of the lives of ordinary Canadians.

"It's everything. You name it, from government services to how companies do their business to how communities help one another -- you need it for all of those things," says Armine Yalnizyan, senior economist for the Canadian Centre for Policy Alternatives. "You hack that out and you've got nothing. You're punching in the dark."

For one thing, commutes could get a lot uglier and junk mail and telemarketers a lot more pervasive without robust census data.

Municipalities use information gleaned from long-form questions on how people get to work and where they work to plan bridges, roads and public transportation projects and budgets, says Derek Cook, research social planner with the City of Calgary.

"We may never again get neighbourhood level statistical data and what the hell are we going to do if we don't have neighbourhood data? How are we going to plan?" he says. "It's like taking a carpenter's hammer away and asking him to go continue to build the house."

This week Ottawa city council voted to petition the federal government to keep the long census form mandatory. "The City of Ottawa and others have depended on this information for many years and without this efficient and effective use of local tax resources they will be seriously compromised in delivery of their mandated services," the motion says.

If more people fill out the long form in the west end than in the east, the city won't have an accurate idea of who needs services and who doesn't, says Councillor Peter Hume. Replicating all the data the census used to provide would be fantastically expensive, and the city couldn't compel people to provide it anyway.

Like Cook and Hume, Brent Toderian, director of city planning for Vancouver, said census data so fundamentally underlie everything a city plans for its residents that he struggles to pinpoint a single instance.

"It's literally the starting point of all of our work, so pick a project," he says, mentioning school boards, new transit lines and aging neighbourhoods as a handful of examples. "The tendrils of this work go all the way through every city in the country."

Marketers use census data to target their mail-out advertising to neighbourhoods where, for instance, there are a lot of families with small children who are more likely to be interested in their product, says Norris at Environics. The system isn't perfect, he concedes, but without reliable demographic data, marketers are more likely to try a scattershot approach, meaning mailboxes crammed with more junk mail and an increase in telemarketing calls as researchers and pollsters attempt to fill in the gaps left by the census.

In recent years, big retailers such as Walmart and Loblaws have started tailoring their inventory to their customers with the help of census data, offering saris and Bollywood movies in stores next to big South Asian communities, for example, or kosher grocery aisles near Jewish neighbourhoods. Many of the retailers to which Canadians flock located where they did or expanded into Canada because census data told them there was a market, Norris says.

Decisions about school programs -- always emotionally fraught for any community -- also rely on census data to get a picture of population trends on the horizon, Norris says.

In Calgary, city officials use long-form census data to head off problems with young people before they start.

City officials had seen the research showing kids left to their own devices between the "critical hours" of 3 p.m. when school ends and 6 p.m. when most parents get home from work are more vulnerable to accidents and injury, alcohol, drugs and criminal activity, but they had no co-ordinated strategy to deal with the issue. They hauled out city maps and long-form census data and what they found surprised them: the most well-known troubled areas of the city were already inundated with programming, but the census data pointed to neighbourhoods no one expected were on the verge of problems.

In fact, the census is the only way to track many of Canada's most pressing social trends and problems, says Ivan Fellegi, former chief statistician at the agency until his retirement in 2008.

After Second World War, it took about 10 years for immigrants to reach the same economic standing as their Canadian-born counterparts, which was "darn good," he says. But in the last 15 or 20 years, that trend has begun to slide and each incoming group of immigrants takes longer than those before them to fully integrate, he says.

Young adults entering the labour market have been on a similar downward trajectory, with each crop of new graduates having a harder time then those before them.

The only reason we know any of that is because of long-form census data, he says, and without comparable data in the future, we won't know if those trends have continued or reversed -- an information gap that's particularly worrying following a global economic meltdown.

And on the hot-button issue of official languages, the long-form census is the only roadmap showing the proportion of people who speak French at home is declining in Quebec, Fellegi says.

"It's a fundamental Canadian social issue, in fact almost an existential issue," he says.

The census is also the only source of detailed information about aboriginals, he says, and it reveals that they're increasing their average education levels, but not really closing the gaps with other Canadians who are becoming more highly educated, too.

"It's a fundamental preoccupation of all of us -- or should be -- to know whether certain very important underlying problems are getting worse or getting better or have stabilized," he says.

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