My main sites have been around since the 90s and so when Google first came out with sitelinks (the expanded type), I didn't have to wait long to see them in most cases.
I launched a new project a few months ago and have gradually allowed the search engines access to different sections of the site. Traffic has been doing nothing but rising very nicely over the past 8 weeks.
Today, I noticed expanded sitelinks for the brand name which is obviously nice :)
Question: When and why does Google display sitelinks? Is it a sign of authority?
I ask because I remember expanded sitelinks being a sign of authority a few years back but a lot has changed since then.
My understanding is that Google awards site links based on the nature of the query and the authority of the site. The query has to be "navigational" in nature. People have to be searching for a brand or a website where there really is only one correct answer. The brand or website has to be popular enough that Google is confident that it is the brand that people are looking for. When Google detects this situation, it puts sitelinks in the SERPs so that users can click directly to a sub-section of the site rather than click through to the home page and then click again to get to the sub-section they need.
To measure the "navigationalness" of a query, Google probably looks at click through rate and how well the domain name matches the query. If one site is getting almost all the clicks and the domain is a close enough match, then the query would be considered navigational.
As far as site popularity goes, I've seen PR 5 sites with sitelinks for their brand. I'm not sure what the threshold is these days, but not all sites get sitelinks. Queries for the brand name also need to be great enough for Google to start calculating whether the query is navigational or not.
A while ago, Google showed in webmaster tools whether you had sitelinks and which pages you had sitelinks for. Back then, my site had two sub-pages with sitelinks. It was weird because they were non-navigational queries and the other pages that Google picked to go with them were not very well related. So clearly there is some other criteria for sitelinks that I don't quite understand, or this was just a case of Google getting it wrong. Today Google doesn't show *which* pages get sitelinks in webmaster tools, so I have little visibility into whether or not I have sitelinks for any sub-pages these days.