Redirects
URL redirection is a process put in place to forward site visitors to an alternative page when the page they are looking to view is no longer live on the site. Redirects may be implemented for migration purposes, as well as for site re-architecture and when pages naturally expire. They can also be used to consolidate ranking signals. Our SEO Office Hours notes below cover the different redirection types and explore how Google understands these.
Further reading: The ABCs of HTTP Status Codes
301 Redirects Pass Full PageRank on a Site Level but Not per URL
If you redirect a full domain, e.g. www to non-www, or http to https, the full authority will be passed over, but individual 301 redirects do not pass the full authority.
Every Step in a Redirect Loses Some PageRank
With redirect chains, some additional authority is lost for each redirect in the chains, so you should minimise them, but the amount is small. Google recommends getting links updated to point directly to the new URL.
302s Will Eventually Be Interpreted as 301s
After a long time, a 302 may be interpreted as a 301.
Canonicalised Pages Stay in Google’s Index
Canonicalised pages may remain showing as indexed for site: searches depending on the ‘site structure’. They are no considered as hard as a redirect, and the page can still surface for unique content. Canonical URLs are not crawled immediately, like a redirect would be. John suggests that if you have a large number of incorrect canonical tags, such as many pages canonicalising to a single page, they might ignore all canonical tags across the site. Google makes a clear recommendation that cleaning up broken canonical tags is a good idea.
Redirecting URLs Do Lose Some PageRank
Changing URLs and using redirects does result in a small loss of PageRank. Keeping original URLs is still better if possible. This is also why Google recommend updating backlinks.