This help page describes how ‘Pages not found’ works as a dimension. See the Pages not found metric for more information.
The ‘Pages not found’ dimension shows URLs that contained an error. This dimension is useful when you want to lower the number of errors that visitor get on your site.
This dimension retrieves data from the
g query strings in image requests. If the
pageType query string equals
g query string (page URL) is recorded. AppMeasurement collects this data using the
pageType variable. If the
pageType variable is not defined or set to anything other than
errorPage, no data for this dimension is collected.
Dimension items include the URLs of pages on your site where an error occurred.