Why this is a problem
Yandex's robot finds documents through links, and the Webmaster Help explicitly states that it may not discover a page with no links pointing to it. A sitemap tells the robot the address, but readers do not browse the sitemap, so an orphan page gets almost no traffic.
Where orphan pages come from
- Old blog articles buried deep in pagination
- Landing pages created for advertising
- Pages whose address has changed while links still point to the old one
How to check your site
Export the addresses from sitemap.xml and compare them with the list the crawler found while crawling the site through links. Addresses that are in the sitemap but not in the crawl are orphans. Each needs a solution: add links to it from related content, merge it with another page via a 301 redirect, or delete it.