October 4 is shaping up to be a consequential day for Atlanta.

On that date, MARTA’s board of directors is expected to vote on a plan to expand the city’s transit network by way of roughly $2.5 billion in tax funds, to be spent over the next four decades.

Exactly how they elect to divvy up that cash, however, is subject to a debate over which parts of Atlanta need mass transit most.

Decisions made this year could help shape Atlanta for generations to come. It’s a big deal. Here’s a primer:

The current project list proposed by MARTA officials includes plans to snake 21 miles of light rail through the city and expand the bus network.

But the most controversial aspect of the transit agency’s current priorities involves the placement of such rail lines.

Roughly four of those 21 miles of streetcar lines are slated to connect MARTA’s Lindbergh Station to Emory University and the Centers for Disease Control and Prevention. It’s called the Clifton Corridor.

Just about everyone agrees the Clifton Corridor is an important project that will pay dividends aplenty. But some worry that funding it could mean shortchanging other necessary additions to Atlanta’s transit system.

Advocates with Beltline Rail Now!, led by Beltline visionary Ryan Gravel and ex-Atlanta City Council President Cathy Woolard, have been fighting to ensure the multi-use trail network has a full 22 miles of light rail alongside its main loop.

But, according to the plans MARTA’s mapped out, only seven miles of light rail lines would be funded by the More MARTA tax funds.

On Twitter especially, Gravel has been using colorful analogies to get his points across.

Activists say the Clifton Corridor, which would cost hundreds of millions of dollars and bring MARTA through land that isn’t even part of Atlanta, shouldn’t take priority over Beltline transit, which was a main selling point when Gravel initially pitched the idea to reinvent the old railroad corridors.

So what can regular Atlantans do right now?

MARTA is currently welcoming community input to help officials decide how to spend its tax cash. Its online survey is open until August 31, and more than 1,700 people have responded thus far, according to the Atlanta Business Chronicle.

To put that in perspective, however, more than 4,800 people have signed Beltline Rail Now!’s petition demanding a complete loop of light rail along the Beltline.

Now, activists like Ryan Gravel hope MARTA will actually heed the input Atlantans are giving.