The mandatory long form census helps shape transit and urban sprawl strategy, says a manager at the City of Toronto's planning department. (Canadian Press)

A top municipal bureaucrat in Toronto says the Harper government's move to replace the mandatory long form census with a voluntary survey will hinder the city's ability to make key planning decisions.

The Conservative government is scrapping the mandatory long form in 2011, calling it an unwelcome intrusion into the private lives of Canadians. All Canadians will still receive a mandatory short census and one in three households will be sent the new voluntary survey as well.

Previously, one in five households were sent the mandatory long-form census.

Tom Ostler, the manager of research and Information at Toronto's city planning department, says the data gleaned from a voluntary survey poses a number of statistical problems.

Voluntary responses skew the data, he told CBC's Metro Morning on Thursday.

It is not yet known if the data taken from the voluntary survey can be cross-tabulated with information taken from the mandatory form in previous years — "a statistician would say you couldn't," he added.

"Also, we're operating in an entire fog here. We do not know what the questions will be on this voluntary long form. We do know that the United States census bureau attempted the same thing in 2003 and abandoned it."

His comments come one day after the resignation of Munir Sheikh, the head of Statistics Canada, who felt the voluntary form would not be an adequate substitute for the mandatory census.

Data key for low-income housing

The city uses some of the information obtained from the long form to inform key decisions like curbing urban sprawl — a key objective of the provincial growth plan for the golden horseshoe region, said Ostler.

For example, one of the long form questions asks for where respondents work. In the last two censuses, there has been a dramatic upturn in the number of people working from home — a trend that informs transit and growth planning, he said.

"It is really important for us to stay on track and track that with future census counts."

The long form survey is also vital in providing data for the construction of low-income housing, he added.

"Only the long form census gives us information on income and affordability," Ostler said.

"The province of Ontario mandates municipalities across Ontario to plan for affordable housing and defines affordability in a way that requires us to have data from the long form census."

Numerous aid groups, health care professionals and economists have cited research that suggests low-income and vulnerable populations are among the groups that are least likely to fill out the long form census.

"They are the ones that we are the most interested in reaching," said Gillian Mason, a vice president at United Way.

"In a voluntary census we wouldn't know who those folks were…and so the most vulnerable populations — the ones that we most need to know about — would not be part of the census."