I have run into confusion about this several times over the past few years. Both are forms of “at-large” election in the sense that they can award the largest organized group every seat in a district (usually but not necessarily the city). Here is how that works.
Take a district of three seats. There are two ways to fill the seats. One is to declare elected the people with the three highest vote totals. This is an “an-large” election in the form of multiple non-transferable vote (MNTV).
Another is to give each seat a number (one, two, or three) and make each candidate choose a number. Then let each voter vote individually for each seat. Then declare elected the highest vote getter under each number.
The ballots might look as follows.
MNTV
Vote for three:
- Bob
- Sue
- Phil
- Amy
- Juan
- Dani
Numbered post
Vote for one per seat:
Seat 1
- Bob
- Sue
Seat 2
- Phil
- Amy
Seat 3
- Juan
- Dani
If Bob, Phil, and Juan get more votes with the first ballot than the other candidates, they win (MNTV or normal at-large).
If Bob gets the most votes for seat 1, Phil gets the most votes for seat 2, and Juan gets the most votes for seat 3, they all win (numbered post).
Both systems therefore can produce the same result in the presence of a cohesive plurality. However, they do so differently, and that difference can be combined (or not) with other institutional designs.