The statistics are comprised of Infometrics data, along with figures from government departments such as Education NZ and the Ministry of Business, Innovation and Employment.
Whanganui's provisional GDP as of December is $1.5 billion, which is an increase of 2.9 per cent on December 2017.
Councillor Alan Taylor recalled BERL previously looking at Whanganui's GDP and finding a figure of around $2.1b, but said there may be a difference in what areas were considered within the district in those findings compared to W&P's report.
"How confident are you that you've got the Whanganui district base there, rather than bits and pieces or other areas that might have bits and pieces of ours?" the councillor asked Fothergill and Ward.
"I think it's fair to say the GDP numbers are a bit of a black art and that's another area that we need to understand better," Fothergill said.
"To give an example, a few of us from the Heads Rd group went and got very, very accurate information about seven years ago to show the income for 86 businesses on Heads Rd was $1 billion, but then when we looked at GDP and percentage figures, it didn't stack up so we know that the $1b was very accurate but it didn't match the GDP when we translate it into those numbers."
Manufacturing contributed $178m to Whanganui's GDP, logistics contributed $51m while agribusiness contributed $113m.
Taylor said the agribusiness figure looked abnormally low for the sector.
"If you spread that out over 1000 farms it looks like a farm gate return of around about $100,000 per farm and that's way below where it should be I would suggest.
"I'm not questioning anything other than saying it is hard to get a really good handle on what's going on here and as long as we can keep using something as a benchmark we can see how we'll progress, but I think it underplays out strength."
Mayor Hamish McDouall was pleased to see a comprehensive report.
"The dashboard is good, dark arts or not, it is good to have those figures there and I guess we'll learn to understand them as we progress."