LOL kind of shocked that all these data people have no clue about March Madness or basketball tournament terms like seeds and sweet 16. Basketball stats are an AMAZING opportunity to explore rich data sets.

For those who need the ELI5 version: In the United States, many large colleges and universities have professional-calibur (but still technically amateur) sports teams that act as a preparation for the high dollar professional sports leagues. In exchange for playing for the school, athletes get free tuition and other perks.

Because there are literally hundreds of colleges and universities in the USA, teams can't play every other school's team. Each school has traditionally associated themselves with an "athletic conference" of approximately the same size of enrollment and geographical area. Each conference has around 10 or 15 teams in it. Schools within the same conference play each other multiple times during the season, so it's pretty easy to determine a conference champion.

So how can you tell what is the 'best college basketball team in the United States?" Since not all conferences are the same size or quality, you can't just look at a team's win-loss record to declare "the best" team. You could use advanced math to rank teams, but people will always clamor for a tournament playoff series to determine bragging rights This is where the National Collegiate Athletic Association, or NCAA tournament comes in.

At the end of the season, typically in March, the NCAA holds a Division I (large school) basketball tournament that people call "March Madness." Who gets invited? We don't know their exact formula, but the NCAA selection committee tries to select the 64 best teams. They definitely always have to invite the conference champions from each conference, plus they then look at coaches polls, journalists opinions, and consider the strength of each conference to give multiple bids (invitations) to powerful conferences.

The 64 teams are divided into 4 regions, and for fairness, each region is going to get a mix of the best and the worst teams. The assignment looks like this:

Rank - Seed - Region #1 - #1 - Region A #2 - #1 - Region B #3 - #1 - Region C #4 - #1 - Region D #5 - #2 - Region A #6 - #2 - Region B #7 - #2 - Region C #8 - #2 - Region D #9 - #3 - Region A #10 - #3 - Region B #11 - #3 - Region C #12 - #3 - Region D #13 - #4 - Region A #14 - #4 - Region B #15 - #4 - Region C #16 - #4 - Region D #17 - #5 - Region A #18 - #5 - Region B #19 - #5 - Region C #20 - #5 - Region D #21 - #6 - Region A #22 - #6 - Region B #23 - #6 - Region C #24 - #6 - Region D #25 - #7 - Region A #26 - #7 - Region B #27 - #7 - Region C #28 - #7 - Region D #29 - #8 - Region A #30 - #8 - Region B #31 - #8 - Region C #32 - #8 - Region D #33 - #9 - Region A #34 - #9 - Region B #35 - #9 - Region C #36 - #9 - Region D #37 - #10 - Region A #38 - #10 - Region B #39 - #10 - Region C #40 - #10 - Region D #41 - #11 - Region A #42 - #11 - Region B #43 - #11 - Region C #44 - #11 - Region D #45 - #12 - Region A #46 - #12 - Region B #47 - #12 - Region C #48 - #12 - Region D #49 - #13 - Region A #50 - #13 - Region B #51 - #13 - Region C #42 - #13 - Region D #53 - #14 - Region A #54 - #14 - Region B #55 - #14 - Region C #56 - #14 - Region D #57 - #15 - Region A #58 - #15 - Region B #59 - #15 - Region C #60 - #15 - Region D #61 - #16 - Region A #62 - #16 - Region B #63 - #16 - Region C #64 - #16 - Region D

As you can see, each region gets a 1, 2, 3... 16 seed . Often these are arranged into a "bracket" see sample bracket picture and people have fun filling out predictions of which teams will win each game.

For each region, the first round is played the same: 1 plays 16, 2 plays 15, 3 plays 14, 4 plays 11, 5 plays 12, 6 plays 10, 7 plays 11, and 8 plays 9. They call this the "round of 64" because there are 64 teams playing amongst the 4 regions.

The second round half the teams are gone, so they call this the "round of 32." After the second round, the teams are very tired, and the winners get about a week off to prepare for round 3

The third round consists of the 16 winners of the previous round paired against each other, so this is called the "SWEET SIXTEEN"

similarly, the fourth round is called the ELITE 8

similarly the fifth round is called the FINAL FOUR

and the sixth matchup, only two teams play to see who is the champion championship.

TLDR: seeds are a proxy for ranking within one of four regions, and the sweet sixteen is the third of six rounds of the single elimination tournament when the sixteen teams remain to compete for the title of "best college basketball teams in the USA" ... Its called "madness" because every year, you will see high-seeded (i.e, underdog) team defeat a low seeded (i.e., powerhouse) team, often at the last seconds of the game.

Now look at OP's chart. A higher y axis indicates more madness, where "worse" seeded teams advanced to the third round. Compare this to the least mad case, where the lowest possible y=40 would indicate that all four #1 seeds advanced, all 2 seeds advanced, all 3 seeds advanced, and all 4 seeds advanced. 1 +1+1+1+ 2+2+2+2+ 3+3+3+3+ 4+4+4+4= 40