Redistribution of the riding boundaries in the Ottawa area are unlikely to cause any significant change in upcoming election results, under a whole bunch of assumptions described below.
Elections Canada reallocated the riding boundaries since the last election. One is lead to inquire about the impact of this redistribution. We approach this problem here in the simplest possible way - consider it a first step.
We have results (votes) by polling district from the 2021 election, as well as the new riding boundaries. For any polling district that lies entirely within a riding we allocate all its votes to the new riding. But if a polling district from the last election is now part of multiple ridings, we allocate that polling districts votes to the new ridings proportionally to the area of the polling district in each new riding.
For example, if a polling district cast 450 votes in the last election, and it has been split among three riding in this election, such that one third of the polling district is in riding A (by area), one sixth in riding B, and one half in riding C, then we’d allocate votes from the last election as 150 to riding A, 75 to riding B, and 225 to riding C. And we do this by party.
Thus we approximate the votes each party would get under the new riding boundaries.
| Riding_2021 | Cons_2021 | Lib_2021 | NDP_2021 | Other_2021 | Riding_2025 | Cons_2025 | Lib_2025 | NDP_2025 | Other_2025 |
|---|---|---|---|---|---|---|---|---|---|
| Glengarry Prescott Russell | 34 | 45 | 11 | 10 | Prescott–Russell–Cumberland | 32 | 45 | 13 | 10 |
| Kanata Carleton | 39 | 41 | 14 | 6 | Kanata | 33 | 43 | 17 | 6 |
| Nepean | 34 | 45 | 16 | 5 | Nepean | 31 | 45 | 19 | 5 |
| Ottawa Centre | 16 | 45 | 33 | 6 | Ottawa Center | 17 | 42 | 34 | 7 |
| Orleans | 29 | 52 | 15 | 5 | Orleans | 27 | 51 | 17 | 5 |
| Ottawa South | 26 | 49 | 19 | 5 | Ottawa South | 25 | 50 | 19 | 6 |
| Ottawa Vanier | 20 | 49 | 24 | 7 | Ottawa Vanier Gloucester | 19 | 48 | 25 | 8 |
| Ottawa West Nepean | 29 | 45 | 19 | 7 | Ottawa West Nepean | 27 | 45 | 22 | 7 |
| Carleton | 50 | 34 | 11 | 5 | Carleton | 48 | 32 | 14 | 6 |
We see that the margin of victory (between winner and runner-up) has increased in six of the ridings, decreased in two, and stayed the same in one. However, in no riding would the boundary change result in a different winner.
Some caveats:
-some Polling Division Number’s had an “A” and a “B”. These were
aggregated by their number, i.e. 103A and 103B were aggregated into
103.
-some polling divisions had no data - I suspect these is a mismatch
between the geography as of the date of the map and the date of the
election data.
-as we were interested primarily in the impact of the geographical
boundary changes, polling districts not associated with any geography
(eg advanced, special polls, etc) have been excluded. This is also why
the results may not exactly match the results from 2021.
- the allocation by area assumes implicitly that within any polling
district the voters are a homogeneous group
- the results presented here assume no change to populating, nor any
factors that may affect voting preferences, Hence it must be considered
only as a first approximation.
- totals may not sum to 100% due to rounding.
All data is publicly available from Elections Canada.