Who is in the field?

The NCAA Tournament is made up of 68 teams. 32 represent the winners of the conference tournaments, while the remaining 36 are at-large teams selected by the NCAA basketball selection committee. There is no limit to the number of teams selected from a single conference, however, there is always at least one.

To be selected as an at-large team, teams must not have won the conference tournament, and they also must be eligible to compete. After that, the process is entirely subjective. Members of the selection committee receive team sheets for each team. On these sheets are a number of relevant, but not required, pieces of information that can be used to judge the team's resume. 

Some of these include:

• NET ranking
• Record
• Road record
• Strength of schedule
• Nonconference strength of schedule
• Average NET ranking for wins and losses
• Advanced metrics like KPI, KenPom, Strength of Record, BPI and Sagarin
• Records against each quadrant
• Outcomes of each game played

Unlike what many may believe, conference record is not a data point committee members use in their evaluation. No one piece is by rule more important than any other, and it is up to individual committee members how they choose to use everything.

The NET replaced the RPI as the committee's official sorting metric, which sorts a team's wins into the four quadrants. These quadrants are based on the opposing team's NET ranking as well as where the games are played. It is not a be-all-end-all number.

Other information not on the team sheets is commonly used. The "eye test," or how a team looks while their playing, is a subjective data point each committee member can use differently. Player injuries are also often taken into consideration, but more so for seeding than selection.

Seeding teams uses the same information as the selection process. After the committee has a list of 68 teams, they put them on what is the S-curve, ranking them from 1-68. Where they are on this list mostly determines their seeding, though they could be moved up or down a line based on bracketing rules.

As teams are placed in the ranking, teams that are near each other can be closely compared in ways that teams ranked further apart aren't. If the committee determines that Team A is ranked 12th and Team B is ranked 13th, but Team B was 2-0 against Team A during the reason, they may choose to but Team B ahead. This wouldn't be taken into consideration if Team A was ranked 12th and Team B was ranked 23rd.

The S-curve is an important tool to ensure regions are balanced once the bracket is constructed. Ideally, the seeded selected as the highest ranked 1 seed would have the lowest ranked 2 seed in their region, while the lowest ranked 1 seed would have the highest ranked 2 seed in theirs. This process snakes through the rankings like an "S" to the best of the committee's ability, though it's never perfect.

Since the field expanded to 68 teams, the last four ranked at-large teams and the last four ranked conference champions play in the First Four in Dayton, Ohio. The conference champions are always 16 seeds, though the at-large teams could be any seed. Typically those games are on the 11 or 12 line, but they have been as low as the 14 line.

While the bracket may seem like it is randomly put together, there are a number of rules the committee must follow when assembling the tournament. Geography is a big one, with teams seed 1-4 given geographic preference in their first and second round locations. The top seeds are also put in the region that is geographically friendliest to them if possible. 

Teams can be placed in first and second round sites nowhere near their regional sites. For example, Team A may be playing in the Midwest region which is hosted in Chicago, but their first and second round location may be in New York. When the matchups are made for the first round, the committee does its best to make sure the higher seeded team isn't at a geographic disadvantage, though this can't be completely avoided. If a school's home court is hosting games, that school cannot play there.

The committee does its best to place team's based on the S-curve, but along with geographic considerations, there are other rules that may make this impossible. If a conference has four or more teams in the top four seed lines, the first four must be placed in different regions. 

Teams from the same conference that have played three times during the season cannot meet until the regional final, while teams that have played twice cannot play each other until the regional semifinal. Conference foes that only met once can meet as early as the second round. Whether they're in the same conference or not, teams that have already played during the season cannot play each other in the first round or First Four if possible.

If they choose to, the committee can move a team up or down a seed line to satisfy this criteria.