The province’s most powerful tribunal will decide how the city will be carved up following a scheduled hearing that began this week.

The fate of the city’s ward boundaries will be decided based on evidence heard in a 95-person capacity room on the 16th floor of a Bay St. office tower that was mostly empty on Tuesday.

That decision of a rare three-member panel of the Ontario Municipal Board, which hears appeals on a broad range of land use planning issues, will determine boundaries for the upcoming 2018 election and beyond.

Here’s what you need to know:

Why are new boundaries important?

A petition from residents challenged the city’s existing ward structure in 2013, which got council’s attention because it raised the possibility of an appeal to the OMB, which has the power to dictate new boundaries.

The city decided to launch what became a more-than-two-year review of the current boundaries, hiring an external team of consultants.

The major consideration in deciding new boundaries is whether residents are being effectively represented. A Supreme Court of Canada decision set out important factors determining effective representation, most importantly voter parity — that all votes should have equal weight.

Today, parts of the city are growing at an unprecedented pace, which has created what the consultants say is a “serious imbalance” in the existing ward population sizes and therefore voter parity — a problem that expected growth only worsens over the next decade.

Adjusting the ward structure is meant to achieve acceptable voter parity while also taking into account other considerations of effective representation like natural boundaries, such as the Don River, and communities of interest, such as Regent Park.

What is the recommended option?

To achieve effective representation, a 47-ward option was recommended by the city’s consultants and approved by council in November.

That option would see four new wards created — three downtown and one in the North York neighbourhood of Willowdale. It would also see one western downtown ward removed. A total of seven wards would see no boundary changes at all.

This structure was designed to create a ward population range of 51,850 to 70,150 and change as little in as many ward boundaries as possible.

Why is there an OMB hearing?

Multiple appeals of council’s ward boundaries decision were filed by residents and also two city councillors — Justin Di Ciano (Ward 5 Etobicoke Lakeshore) and Giorgio Mammoliti (Ward 7 York West).

Some appellants have very specific requests for redrawing lines in their part of the city. Others have raised broader concerns about the consultative process. Several, like Di Ciano (who missed the November council vote) are arguing that a 25-ward structure that follows federal riding boundaries should be adopted instead.

What are the options?

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The city’s consultants considered several other options include creating 58 smaller wards and a 25-ward option aligned with federal riding boundaries.

Most of these options, including the 25-ward option, were discounted by the city’s consultants because they did not achieve acceptable voter parity without significant adjustments.

What do the appeals mean for Toronto residents?

Most significantly, the new boundaries would shake up the election and a future council in two ways:

New downtown wards give candidates that have been trying to break into downtown wards — several people have been waiting in the wings for years — more opportunities to run for open seats, as well as an open seat in Willowdale

Incumbents in Mayor John Tory’s inner circle would be pitted against one another with the loss of a downtown ward in the area where Councillors Ana Bailao and Cesar Palacio currently hold seats along with Gord Perks, one of Tory’s most vocal critics

If the OMB rules against the city’s decision, it could be sent back to council for further review — which means new boundaries are unlikely to be in place for the 2018 election — or the OMB could dictate new boundaries, which may shake-up more election races or separate longstanding communities.

When will a decision be made?

The city’s clerk has made clear that in order to make sure everything is properly in place before the Oct. 22 election next year, a decision on boundaries needs to be finalized by Dec. 31.

Though Councillors Di Ciano and Mammoliti originally tried to have the timing pushed back, the city’s lawyer Brendan O’Callaghan succeeded in convincing the OMB members to hear the matter as soon as possible.

The hearing is scheduled for nine days with a decision expected before Dec. 31.