Even more so than the National Party, New Zealand First relied on a handful of seats to deliver the bulk of their party vote this election.
In terms of New Zealand First's most valuable electorates, there's nothing particularly surprising here. Whangarei benefited from Shane Jones' high profile candidacy, while Winston Peters himself helped New Zealand First slightly grow its share of the party vote in Northland. Tauranga, Bay of Plenty, and Coromandel probably benefit from higher than average numbers of voters aged over 65, and for the first two probably a bit of legacy support for when that was Winston Peters' voter base. Waiarapa also has an above average grey voter base, but also features New Zealand First's deputy leader, Ron Mark. While Rodney has their former deputy leader and relatively high profile MP Tracey Martin as their candidate, which are also likely to be factors.
Of note, New Zealand First only managed to grow their share of the party vote in three other electorates - Clutha-Southland, West Coast-Tasman, and Tukituki.
Of those three other electorates where New Zealand First grew their share of the party vote, none of them ran New Zealand First candidates back in 2014, so there's possibly a lesson there about ensuring you run candidates in as many electorates as possible to maximise your exposure.
The other area where New Zealand First's most valuable electorates echoes National's top electorates is that they're all high turnout electorates, and actually average a slightly higher turnout than National did.
As for New Zealand First's least valuable electorates, nothing here particularly stands out either. It doesn't surprise me that the more cosmopolitan parts of New Zealand are also the least likely to vote for New Zealand First. No guesses for why that might be either.
Electorate strength for New Zealand First clearly depends on both the popularity of Winston Peters, but also the ability of high profile candidates to turn out older voters in support of the party. This strength is also their greatest weakness. The party's existence seems to largely depend on Winston Peters own fortunes, and if they're down, then the party is out, so closely are the two brands aligned.
As to what opportunities that presents for New Zealand First at the electorate level? It's a hard one. If we assume that Winston Peters is going to contest the 2020 election (and it's entirely possible he might), then New Zealand First needs to identify electorates that share characteristics with their 10 most valuable and maximise their party votes there too. Some possibilities include Kaikoura, Ōtaki, Waitaki and Rangitata. These electorates also represent an opportunity for New Zealand First to transform itself from a platform for Winston Peters into a party representing rural New Zealand, a niche exploited relatively well by the Nationals in Australia.