This is the ninth in a series that will run until the end of the campaign, taking an in-depth look at where the polls stand in every region of the country and which seats are up for grabs. Check out the last instalment, where the spotlight was on francophone Quebec.

The province to vote last may have the last word.

British Columbia's 42 seats will play a vital role in this election, considering that as many as two-thirds of them are up for grabs.

The province was not nearly the battleground in 2011 that it is in 2015. The Conservatives dominated B.C. four years ago with 45.5 per cent support, winning 21 of the 36 seats the province had at the time. The New Democrats finished second with 32.5 per cent support and 12 seats, while the Liberals took just 13.4 per cent and two seats. The Greens captured 7.7 per cent of the vote, and Elizabeth May was elected in her riding on Vancouver Island.

From that Conservative blowout, B.C. has now become a tight three-way race. The Liberals narrowly lead in the Poll Tracker with 31 per cent, followed by the Conservatives at 28.7 per cent and the New Democrats at 28 per cent. The Greens have averaged 10.7 per cent in recent polls.

The race has been incredibly close provincewide since the end of September, a shift from the only marginally less tight three-way race that gripped the province from the end of August.

But that, too, was a shift from where things were at the campaign's outset. At the time, the New Democrats were leading with about 40 per cent, with the Conservatives and Liberals at 28 and 23 per cent, respectively. The Conservatives, Greens, and especially the Liberals have benefited from the NDP's drop in the province.

Regional and riding level polling, however, suggests a series of battlegrounds in B.C. In the Interior and north, the race is primarily between the New Democrats and Conservatives. The New Democrats are on top on Vancouver Island, but are under pressure from a Green Party that has posted at least 21 per cent in every poll conducted during the campaign. Vancouver and the Lower Mainland, meanwhile, have a three-way race, with the Liberals narrowly ahead in some key ridings.

At current levels of support, the Conservatives would likely win the most seats, about 11 to 19. The NDP would win between 11 and 18 and the Liberals between 10 and 14, a division that suggests B.C. could be the most evenly multi-coloured province in the country after Oct. 19.

But with one week to go in a close three-way contest, there are many more ridings that could potentially be in play on election night.

The following is a list of ridings that each of the parties could pick up on election night. Favourable gains are those in which there is a good chance of the party winning, potential gains are those in which the results may be close and marginal gains are seats in which the party has an outside chance.

For the Conservatives, who are potentially in play in as many as 32 ridings in the province, their minimum expectations will be to hold their seats in the Fraser Valley and the southern Interior. But a better night will see them holding on to some of their seats in the suburbs around Vancouver, particularly in Surrey, and picking off a few of the weaker NDP seats. A strong night for the Tories would see the party holding off the New Democrats on Vancouver Island and sweeping the six new seats added to the electoral map.

Favourable Conservative gains:

Cloverdale-Langley City.

Mission-Matsqui-Fraser Canyon.

Potential Conservative gains:

Burnaby North-Seymour.

South Okanagan-West Kootenay.

Marginal Conservative gains:

Burnaby South.

Cowichan-Malahat-Langford.

Delta.

Esquimalt-Saanich-Sooke.

Nanaimo-Ladysmith.

Port Moody-Coquitlam.

Surrey Centre.

Vancouver Granville.

The New Democrats are in play in 26 ridings across the province, with potential for gains (and losses) from one end of B.C. to the other. At the very least, the New Democrats will be looking to maintain their strongholds in Burnaby, on Vancouver Island and in Vancouver. But a decent showing would see them making gains on Vancouver Island at the expense of the Conservatives, as well as in the Fraser Valley. A very strong night would see them making gains in the Interior, sweeping Vancouver Island (with the exception of Elizabeth May), and making gains in Surrey and deeper into the Fraser Valley.

Favourable NDP gains:

Burnaby South.

Nanaimo-Ladysmith.

North Island-Powell River.

Potential NDP gains:

Courtenay-Alberni.

Kootenay-Columbia.

Pitt Meadows-Maple Ridge.

Marginal NDP gains:

Cariboo-Prince George.

Coquitlam-Port Coquitlam.

Delta.

Fleetwood-Port Kells.

Kamloops-Thompson-Cariboo.

Mission-Matsqui-Fraser Canyon.

North Okanagan-Shuswap.

Steveston-Richmond East.

Vancouver Granville.

The Liberals have less upside in British Columbia than the other two major parties, but are potentially in play in 16 ridings. Winning even half that number would be a decent showing for a party that has struggled in the province in recent elections.

Gains for the Liberals will come almost entirely in and around Vancouver. The lowest hanging fruit is in Vancouver itself and neighbouring Richmond, while a stronger showing for the Liberals would see them moving into Surrey and Burnaby as well.

Favourable Liberal gains:

Delta.

North Vancouver.

Steveston-Richmond East.

Surrey-Newton.

Vancouver Granville.

Vancouver South.

West Vancouver-Sunshine Coast-Sea to Sky Country.

Potential Liberal gains:

Burnaby North–Seymour.

Fleetwood–Port Kells.

Richmond Centre.

South Surrey–White Rock.

Surrey Centre.

Marginal Liberal gains:

Cloverdale-Langley City.

Vancouver Kingsway.

The Greens cannot be discounted in B.C., particularly on Vancouver Island. The best hope for a second Green MP in B.C. is likely in Victoria, while the Greens have a very marginal shot in ridings like Esquimalt-Saanich-Sooke and Nanaimo-Ladysmith.

How big of an impact might British Columbia have on the election outcome? It could be significant. If the NDP performs better than expected in the East, results on the West Coast could tip the balance for them.

And depending on how they swing, those seats on the bubble in B.C. could be the difference between the Liberals and Conservatives coming out on top in the national seat count.

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CBC's Poll Tracker aggregates all publicly released polls, weighing them by sample size, date and the polling firm's accuracy record. Upper and lower ranges are based on how polls have performed in other recent elections. The seat projection model makes individual projections for all ridings in the country, based on regional shifts in support since the 2011 election and taking into account other factors such as incumbency. The projections are subject to the margins of error of the opinion polls included in the model, as well as the unpredictable nature of politics at the riding level. The polls included in the model vary in size, date and method, and have not been individually verified by the CBC. You can read the full methodology here.