What is Display lost IS (rank)?

The column is labelled Display lost IS (rank) in the interface. Its Search counterpart, search lost IS (rank), is the percentage of time that your ads weren't shown on the Search Network due to poor Ad Rank in the auction. Same shape, different network. Google reports impression share metrics separately for each campaign type and does not aggregate them across the account, so a Display campaign's rank loss is not a reading of a Search campaign's.

The trap is the one the Search column has. Google's note, that Lost IS (rank) won't be shown on your Ad groups tab if you ran out of budget at any point during the date range being examined, sits under both columns. Our reading: if the campaign ran out of budget on even one day of the window, a blank at ad group level is a missing measurement, not a healthy Ad Rank.

For Display Network campaigns, Google's tips for improving impression share say one of the best things you can do is improve your display ad quality, and suggest adjusting your managed placements, the Display Network websites or subsets of websites where you'd like your ad to appear. They do not map either tip to a particular loss column. Google also warns that if you decrease the number of your placements, you may see an increase in impression share, but the size of the "pie" has been reduced. Our reading: after cutting placements, read the share beside the absolute impression count before calling it progress.