Last tested; Jan 13, 2021
The short explanation is that with Ordinal Scale Type setting, data is plotted along the x-axis as evenly-spaced, discrete entries, regardless of relative distance between data points. (https://docs.looker.com/exploring-data/visualizing-query-results/column-options#scale_type)The longer explanation:
Let’s say you have a dataset like the following, where you have a gap in data from December 26th to December 27th (December 25th has data as shown in the data table, it looks empty here because it is a small number for the scale of this visualization).
If you would like to show your data over the full timeframe that the data was collected, you can use the “Automatic based on Data” Scale Type (as shown above), or the “Time” Scale Type. However, if you do not want to show this gap, the Ordinal Scale Type will only plot the data from the data table.