Four metro school districts -- Atlanta, Decatur, DeKalb County and Fulton County -- are linked by overlapping boundaries and state law when it comes to sales taxes to fund school projects. Fulton can't put an education sales tax on the ballot unless Atlanta does. And Atlanta, Decatur or DeKalb can't go to voters  alone.  Each district has had sales taxes three times since the late 1990s. In November, the districts plan to ask voters to approve their respective fourth, five-year sales tax.

If voters agree, money will roll through June 2017. Sales taxes, even in a shaky economy, bring in big money. Collectively, the four school districts expect to have raised nearly $1.6 billion by the time the current, five-year 1-percent tax expires. They're expecting the next sales tax could bring in a combined total of about $1.9 billion to build new schools, renovate others and buy technology.

Here's what each school system expects to collect by the time the current tax expires next June: DeKalb, $466 million; Decatur, $11.9 million; Atlanta, $429 million; and Fulton,  $680 million. The economic downturn resulted in less revenue across the board.

When will the new school tax start and end? Start July 2012 and end June 2017

How much will a five-year extension bring?

DeKalb, $477 million; Fulton, $912.4 million; Decatur, $18 million; Atlanta, $513.4 million

What's most expensive project proposed by district?

DeKalb County -- A new Chamblee High School, $58.7 million

Fulton County -- A new McNair Middle School, $39.8 million; and a new technology plan, $189 million.

Decatur -- Officials say cost estimates are still being developed.

Atlanta -- A new Sylvan Middle School, $28.7 million.  (This project, like others, is contingent on a demographic study to be conducted later this year, the results of which could have an impact on planned school construction projects.)

Each system's enrollment in 2011 and 2017, when the new tax ends:

Atlanta -- 45,582 for 2011-2011 and 46,978 for 2016-2017

DeKalb --  98,000 currently, dropping 500 students a year to about 95,000 in 2017;

Fulton -- 91,671 currently, up to 99,819 in 2016-2017 school year

Decatur --  2,092 for FY 2011, growing to 3,686 by 2015

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Major plans by district:

Atlanta Public Schools

Construction and renovation of schools (including some rolled over from sales tax III)  -- $245 million

Upgrading building infrastructure and systems -- $80 million

Security and safety system upgrades -- $16 million

Upgrades for athletic fields and playgrounds -- $21.4 million

Buying property (including land for new elementary, new high school in North Atlanta) -- $58 million

Technology upgrades -- $56 million

Fulton County Schools

Building 10 new schools -- one elementary north ($21.9 million), one middle school north ($34.6 million) and two elementary schools south, replacements for Gullatt Elementary ($22.5 million), Esther Jackson Elementary ($23.8 million), Heards Ferry Elementary ($21.9 million) and McNair Middle School ($39.8 million) and closing four elementary schools (College Park, Harriet Tubman, Mount Olive and Oak Knoll and building two in their place at a cost of $23.6 million each )

Renovating 69 schools -- $227 million

Technology -- $189 million

Decatur City Schools**

Acquire the property currently being leased for the 4-5 Academy at Fifth Avenue, the new school slated to open in August to fourth and fifth graders, and for the College Heights Early Learning Center.

Convert a gymnasium to classrooms at Renfroe Middle School and make other improvements.

Renovate and repair facilities, including Clairemont Elementary School, College Heights Early Childhood Learning Center, Decatur High School, the 4-5 Academy at Fifth Avenue, Glennwood Elementary School, Oakhurst Elementary School, Renfroe Middle School, Westchester Elementary School, and Winnona Park Elementary School.

Technology upgrades, buses and facility repairs throughout the district.

DeKalb County Schools

Building new elementary schools each costing $20.6 million -- Fernbank, Gresham Park, Peachcrest, Pleasantdale, Rock Bridge and Smoke Rise

Technology -- $42.7 million

Replace Chamblee High School $58.7 million; replace McNair Middle School $37.4 million

Renovations and additions, including at Redan High ($22.4 million) and Henderson Middle School ($16 million)

Arts school at Avondale High School $4.3 million

Source: Atlanta Public Schools, Fulton County Schools, City of Decatur Schools, DeKalb County School System

**Decatur school officials said cost estimates on individual projects are not available

Other upcoming sales tax votes:

Cherokee: A vote is on the ballot for Nov. 8, which would extend the current tax for five years.

Gwinnett: A vote could be held as early as November, but nothing is official yet. The school system's current tax began July 1, 2007 and expires June 30, 2012.