ZACHARY — A preliminary look at 2010 census figures shows that the five council districts fail to comply with the “one-man, one-vote” concept of equal representation, a demographer told the City Council.

Troy C. Blanchard of LSU gave the mayor and council a brief overview Tuesday of the redistricting process required for public bodies after a federal census.

Zachary switched from at-large balloting for council members to single-member districts with the fall 2006 elections. The same districts were used again for the 2010 elections.

Blanchard said the 2010 census put Zachary’s population at 14,960, which would mean that each council member should represent 2,992 residents in an “ideal district.”

A deviation of 5 percent above or below that number would be acceptable, he said.

Blanchard, who said he is not doing a redistricting plan for the city, nevertheless applied the new census data to Zachary’s current districts.

He found that districts 1, 2 and 3 deviate above 2,992 by 11.6, 7.7 and 21.4 percent, respectively.

Districts 4 and 5 are below the ideal population by 21.8 and 18.9 percent, respectively.

“Just based on this, it looks like every district is going to have to give or take some people. It looks like a very complex process,” Blanchard said.

Blanchard said districts 4 and 5 may not have lost population between 2000 and 2010, but the negative deviation may have more to do with faster growth in districts 1,2 and 3 on the west side of the city.

Nancy Jensen, one of the demographers who drew the current lines, said Zachary’s growth spurt between the two censuses may have made the districting plan out-of-date when it was accepted in 2005.

However, the city was forced to either use the 2000 census numbers or pay a steep price for an independent census in the middle of the decade that the U.S. Department of Justice would accept, she said.

Zachary’s next council elections are in 2014.

Blanchard also provided the council with some population estimates out to 2019, when he said the city should have nearly 20,400 residents.

During the 10-year period, 2010-19, the city will have a high growth rate for adults ages 25 to 40.

“The question is: will they stay?” Blanchard said.

Blanchard also forecast a high rate of growth for children in the same period.

In 2019, about one in every three people will be a child between 3 and 17 years old, compared to about one in five in 2007.

Noting that the proposed Americana residential-commercial complex is expected to have a movie theater, Blanchard said it may be a good thing.

“We’re going to have a huge bunch of kids running around,” he said.