Data tables are row-by-column matrices, and obviously they can range in size from one row by one column to many rows by many columns. You might have come across the colloquial expressions narrow table and wide table, or even narrow long table and wide short table. These concepts refer to the number of columns in the table, but not in a literal sense.

They refer to the fundamental way in which the data is structured or categorized in a table. In a basic narrow table, a list of categories is contained under a single column and a second column lists values associated with each of those categories: just two columns, but potentially many rows. In reality, there may be other reference columns, but the basic concept holds: one column containing all values across categories. In a basic wide table, each category gets its own column and the associated values appear under it: potentially a lot of columns and as few as one row.

Consider the GDP data...