Tall data describes a structure in which each distinct measure in a row is contained in a single column. Tall data often results in more rows and fewer columns.

Consider the following table, which represents the same data as earlier, but in a tall structure:

Now, we have more rows (a row for each year for each country). Individual years are no longer separate columns and population measurements are no longer spread across those columns. Instead, one single column gives us a dimension of Year and another single column gives the measure of Population. The number of rows has increased while the number of columns has decreased. Now, the measure of population is at the same level of detail as the individual row, and so visual analysis in Tableau will be much easier.