Google has updated how they calculate the clicks and impressions in the Search Analytics report within the Google Search Console. Google updated their data anomalies page, explaining:
We refined our standards for calculating clicks and impressions. As a result, you may see a change in the click, impression, and CTR values in the Search Analytics report. A significant part of this change will affect website properties with associated mobile app properties. Specifically, it involves accounting for clicks and impressions only to the associated application property rather than to the website.
If you log into your Google Search Console account, you will see a line that reads “update” in your Search Analytics report. That line represents that going forward, past April 26, the new metrics come into play.
Google’s John Mueller added some additional insight on Google+, explaining, “Other changes include how we count links shown in the Knowledge Panel, in various Rich Snippets, and in the local results in Search (which are now all counted as URL impressions).”
He added what it means for URLs to show up and be counted:
FWIW one question that has come up a few times regarding Search Analytics is how local results are handled. Luckily, it’s pretty straightforward: if a URL from your site is included in the local result, it’s counted as an impression. If the same URL is included multiple times (e.g., multiple franchises in the same area with a shared web URL), that URL is just counted once. If a local result (w/web link) + a natural web result are included in the same results page, then that’s counted as 1 site impression (which is used for the view by query, for example), and the URLs individually get the page impressions (which is used in the per-page view).
Most people shouldn’t see a significant change in their Search Analytics report, but Google did add that mobile apps might show the largest discrepancy.