Matrices have a field called Contents, where you can set the type of information that is stored: travel times, tolls, parking slots etc.

Click to enlarge: Set the type of information that is stored
You can use the Contents to group matrices into subfolders, which is particularly convenient when working with multiple matrices:

Click to enlarge: Group matrices into subfolders

Click to enlarge: Multiple matrices
Aimsun uses the Contents to filter through all the matrices and find those that can be used in a given context. For example, in the Distribution Scenario editor, the combo for Skim matrices lists only the matrices with the appropriate User Class and Contents equal to Cost, Distance, Travel Time, Speed or Toll:

Click to enlarge: Aimsun uses the Contents to filter through all the matrices
It’s important that you make sure you set the matrix Contents correctly, otherwise you may not be able to select them when you need to later on. For example, if you want to use a matrix as Max Deviation Matrix in a Static OD Adjustment, you have to set its Contents as Max Deviation:

Click to enlarge: To use a matrix as Max Deviation Matrix in a Static OD Adjustment, set its Contents as Max Deviation
You can set the Contents to one of the following options:
- Not Set: when no option has been selected; default when creating a new matrix, or for skim matrices based on Function Components (whose content cannot be figured out automatically by Aimsun)
- Trips: OD matrices containing vehicle trips between zones; they can be used in Traffic Demands
- Costs: skim matrices that provide the total generalised cost, the PT fare, the PT in-vehicle time, the PT crowding discomfort, the PT transfer penalty, the PT waiting time and the PT walking time between zones
- Travel Times: available for the user to manually set the Contents of a skim matrix based on a Function Component
- Distances: skim matrices that provide the distance between zones
- Tolls: available for the user to manually set the Contents of a skim matrix based on a Function Component
- Arrivals Departures: not used
- Generation/Attraction: not used
- Parking Slots: not used
- Blocked Cells: used to set the OD pairs zero in a cell means “blocked” and any non-zero value means “blocked”, in order to set the cells that should contain no trips in the matrices produced by Distribution/Mode Split
- Distribution: Through Traffic: used to provide the trips between external zones, which are added to the matrices produced by Distribution/Mode Split
- Junction Delay: not used
- Individuals: OD matrices containing person trips between zones; once divided by vehicle occupancy, they become trip matrices
- Speed: available for the user to manually set the Contents of a skim matrix based on a Function Component
- Ratio: not used
- Max Deviation: used in OD Adjustment to constrain the change it can apply to each cell; zero means “Frozen”