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Just over one in three of the 338 ridings being contested in October's federal general election will be either new, or will have unfamiliar or no sitting MPs running in them by the time the writ is dropped.

Join Nanos Research's Greg Weston, author Susan Delacourt, and me at today's Canadian Club lunch panel called "Campaign Countdown". Details can be found here.

Add that to the current three-way poll standings of Canada's major national parties, and it will make for a highly competitive and very unpredictable election campaign in the fall.

To this point, it's always been assumed that the new riding boundaries, and particularly the existence of the 30 new seats, would favour the Conservatives and their bid for re-election with a majority government.

However, to win another majority government, the blue team would have to keep all 159 of its current seats, and add at least 15 of the 30 new ridings – which will be harder to do with fewer incumbents and others fleeing for safer ground.

The stakes are equally high for the opposition New Democrats who are aiming to prove that 2011 was not a fluke, and for the Liberals who are desperate to prove the opposite.

Consider:

• There are 30 new seats being added to the Chamber in October. Of those, 13 ridings will be contested by sitting MPs who have represented little or none of the geography they comprise (9 Conservatives, 3 NDPers, and 1 Liberal).
• Six more Conservative MPs have switched into other ridings due to changing boundaries and improved prospects (3 in Alberta, 2 in Saskatchewan, and 1 on Vancouver Island), while another Liberal MP is currently in the process of trying to do the same (Eve Adams in Eglinton-Lawrence).
• At least 48 sitting MPs will not be on the ballot in October (27 CPC, 11 NDP, 5 Lib, 1 BQ + 4 Independents), including two who were defeated for their nomination; and that figure is not even counting:
  • the 4 currently vacant seats (2 CPC, 1 CPC-turned-Ind, 1 NDP-turned-Ind)
  • the 2 NDP MPs who have been defeated for their nominations but haven't announced their future plans yet (Benskin and Raynault)
  • the 2 NDP MPs who may yet be challenged for their nominations (Genest and Nunez-Melo)
  • the 2 Conservative MPs (Fantino and Yelich), 1 NDPer (Bevington) and 1 Independent (Scott Andrews) who have yet to announce their intentions at all
• As a result, 20 further ridings have been vacated by the 13 MPs running in the new ridings, 6 running in different ridings and 1 trying to.
• 5 ridings will feature the same MP running, but under a different banner than 2011 (Mourani for the NDP, Hyer for the Greens, Rathgeber as an Independent, and the 2 Forces et Democratie MPs Fortin and Larose).

To put it another way: as many as 97 ridings – new and old – will not be contested by a sitting MP, and a further 18 will be contested by sitting MPs in either a new riding or a new party.

Sixty seems like current ceiling of resigned, retiring and defeated MPs for the current cycle, but as we've already seen, 13 MPs have already stepped down after being nominated for the current cycle, so there's a chance we could see a few more resignations between now and the fall. We're currently 12 shy of the recent record set in 1993, where 72 MPs did not re-offer, but then there was no redistribution in 1993 to add or change seats either.

Definitions

Defining what constitutes a "new" or "different" riding can get bogged down quickly with a lot of details. The definition of a "new riding" I've used here is any riding that is not the "primary successor" of any old riding. If the majority of the population of an old riding goes to a new riding, that new riding is its primary successor in this methodology. Pick the primary successor riding of each old riding, and the 30 you're left with are the new ridings so far as I'm concerned. Sometimes it's a close call, but you have to pick one. And of course the current MP might not live in the primary successor riding, and might want to switch.

But that does leave a couple of cases where the "new" riding has the same name as a previous riding that is not its primary successor. In the current round, the new Markham-Unionville is not the most populous descendant of the old Markham-Unionville, and indeed its current MP (John McCallum) is nominated to run for the Liberals in Markham-Thornhill instead. Same goes for Calgary Nose Hill.

An "open seat" is one that has no sitting Members of Parliament running in it. A sitting MP can switch and run in a different riding – but in that case is she or he the "incumbent" Member of Parliament? Hard to say, but I bet a lot of us will fall back on that term as a convenient short-hand.

Then there's the issue of "party incumbency" in a seat. I think we can agree that Mount Royal is an open Liberal seat, just as Winnipeg South is an open Conservative seat or Vancouver East is an open NDP seat. But what about Winnipeg North? It's listed as a nominal win for the NDP in the 2011 Transposition, but its incumbent MP is running for re-election is a Liberal.

Or here's an even more complicated one for you: Maria Mourani is running in Ahuntsic-Cartierville, which is listed as a nominal win for the Liberals, but she was last elected as a member of Bloc Quebecois in its primary successor riding of Ahuntsic, and is now nominated to run in the successor riding for the NDP. Enough to make your head spin.

To help, I try to distinguish between nominal wins, the MP's party banner last elected under, last sitting as, and so forth.

[Click on image to open full-sized PDF table]

Looking by region, the new and open (or potentially open) seats break down this way:

Atlantic

Five open seats (and perhaps a sixth) from MP retirements: 2 Conservatives (Keddy and Kerr) in Nova Scotia, a Conservative (Allen) and NDPer (Godin) in New Brunswick, and a Liberal (Byrne) along with possible a Liberal-turned-Independent (Andrews) in Newfoundland & Labrador.

Quebec

Three new seats: 2 with sitting NDP MPs switching in to run in them (Giguere in Thérèse-De Blainville, and Freeman in Mirabel), and a third remaining as an open seat (La Prairie on the south shore of Montreal).

Two open seats as a result of those MPs switching ridings.

Eleven sitting MPs retiring, leaving open seats: 1 Conservative (Paradis), 4 NDP (Latendresse, M-C Morin, Jacob, Brahmi), 1 Lib (Cotler), 1 NDP-turned-Lib (St-Denis), 1 NDP-turned BQ (Patry), 1 NDP-turned-Independent (Hassainia), 1 Lib-turned-Ind (Pacetti), and 1 BQ-turned-Ind (Bellavance).

Three NDP MPs losing a contested nomination: Morin in Laurentides—Labelle, Benskin in Ville-Marie—Le Sud-Ouest—Île-des-Soeurs, and Raynault in Joliette

Two further NDP MPs who are either currently facing a nomination challenge (Nunez Melo in the Laval riding of Vimy), or are rumoured to be.(Rejean Genest in Shefford).

Three MPs running under a different banner (Mourani in Ahuntsic-Cartierville, and the two F+D folks in Avignon and Repentigny).

Ontario

Fifteen new seats, with 7 sitting Conservative MPs (Daniel, Gosal, Kramp, Menegakis, Raitt, Seeback and Sweet) and 1 Liberal (Freeland) switching to run in them, leaving 7 others as open seats (1 of which – Markham-Unionville –  uses an old riding's name).

Four vacant seats: Peterborough–Kawartha (Del Mastro), Sudbury (Thibeault), and Ottawa West-Nepean (Baird) – all with by-elections now ongoing – and also Patrick Brown's recently vacated seat of Barrie-Innisfall.

Ten sitting MPs retiring in the fall, leaving open seats: 6 Conservatives (Davidson, Devolin, Norlock, O'Connor, Preston and Schellenberger), 2 Liberals (Hsu, Valeriote), and 2 NDPers (Charlton, Comartin).

One MP yet to make clear if he's running again: Fantino for the Conservatives in Vaughan-Woodbridge.

One MP trying to win a nomination in a different riding: former Conservative Adams for the Liberals in Eglinton-Lawrence.

One MP running under a different banner than 2011: former NDPer Hyer for the Greens in Thunder Bay-Superior North.

Eight ridings vacated by the sitting MPs who are nominated to run in new ridings:

Manitoba

Three sitting Conservative MPs retiring in the fall, leaving open seats (Bruinooge, Glover, Smith).

Saskatchewan

Four sitting Conservative MPs retiring in the fall, leaving open seats (Boughen, Breitkrauz, Kormanicki and Vellacott).

Two sitting Conservative MPs who've switched ridings – or more precisely, picked the more rural of their options after the major boundary changes, and their colleagues' retirement intentions were made known (Block, Lukiwski), and leaving the more urban of their options as open seats,

One MP who has yet to make clear if she's running again (Yelich).

Alberta

Six new seats, with 1 sitting Conservative MP switching to run in it (Lake), and 5 that will remain open seats (1 of which – Calgary Nose Hill –  uses an old riding's name).

Four sitting Conservative MPs retiring in the fall, leaving open seats (Ablonczy, Goldring, Hawn, Payne).

One sitting Conservative MP who announced his retirement, but could have run in either the open new seat of Peace River—Westlock or in the open seat of Lakeland, but did neither (Storseth).

One sitting Conservative MP who lost a nomination bid (twice) to run in the fall (Anders).

One sitting Conservative-turned-Independent MP who will run as an Independent instead this fall (Rathgeber).

Four ridings vacated by sitting MPs who are nominated to run in different ridings (Ambrose, Hillyer, Rempel, Uppal).

British Columbia

Six new seats, with 1 Conservative (Findlay) and 1 NDPer (Stewart) switching to run in them, and 4 others remaining as open seats.

Seven sitting MPs retiring in the fall, leaving open seats: 4 Conservatives (Harris, Hiebert, Kamp, Mayes) and 3 NDPers (Atamanenko, Crowder, Davies).

One sitting Conservative-turned-Independent MP who is retiring in the fall (Lunney), but whose seat is being backfilled by another Conservative MP (Duncan).

Two ridings vacated by sitting MPs who are nominated to run in new ridings: (1 Conservative – Findlay, and 1 NDPer – Kennedy Stewart).

One other riding vacated by a sitting Conservative MP (Duncan), who has been nominated to run in a neighbouring open seat from a retirement memner.

North of 60

Sitting NDP MP Dennis Bevington has yet to announce his intentions regarding another bid for office this fall.