The columns of dimension tables give the measures from the fact tables context, such as Internet Net Sales by sales territory country and calendar year. More advanced dimension columns, such as the Customer History Segment column, described in Chapter 2, Connecting to Sources and Transforming Data with M, can instantly give report visualizations meaning and insight. In addition to their application within report visuals, such as the date axis of charts, dimension columns are frequently used to set the filter conditions of a report, a report page, or a specific visual of a report page. By default, Power BI lists dimension tables alphabetically in the fields list and also lists column names of tables alphabetically.

Just as dataset designers must ensure that all common DAX Measures are included in the dataset, dataset designers must also ensure that the necessary dimension columns are available to group, filter, and generally interact with the dataset. Two of the top usability features for dimension tables include hierarchies and custom sorting. When implemented, these features enable users to explore datasets more easily, such as drilling up, down, and through the columns of a hierarchy. Additionally, the sort by column feature serves to generate logical report layouts, such as the months of the year from January through December.