Difference Between a Column and a Line Chart

With simple column charts, life is easy. It doesn't matter too much what data you choose to use for your category axis because your choice simply changes the way data's grouped. Other chart types that follow the same principle include pie charts (which only allow one series), bar charts (like column charts, but oriented horizontally instead of vertically), and donut charts (where each series is a separate ring).

The same isn't true for line charts and most other types of Excel charts. The category axis you use for a line chart is important because the values in each series are connected (in this case, with a line). This line suggests some sort of "movement" or transition as values move from one category to another. That means it makes sense to use a line to connect different dates in a region (showing how sales have changed over time), but it probably doesn't make sense to use a line to connect different regions for each date. Technically, this latter scenario should show how yearly sales vary as you move from region to region, but it's just too counter intuitive for anyone to interpret it properly.

As a general rule of thumb, use time or date values for the category axis. You should do this especially for chart types like line and area, which usually show how things change over time.