GOOGLE CRAWLING AND INDEXING

Finding information by crawling

We use software known as “web crawlers” to discover publicly available webpages. The most well-known crawler is called “Googlebot.” Crawlers look at webpages and follow links on those pages, much like you would if you were browsing content on the web. They go from link to link and bring data about those webpages back to Google’s servers.

The crawl process begins with a list of web addresses from past crawls and sitemaps provided by website owners. As our crawlers visit these websites, they look for links for other pages to visit. The software pays special attention to new sites, changes to existing sites and dead links.

Computer programs determine which sites to crawl, how often, and how many pages to fetch from each site. Google doesn't accept payment to crawl a site more frequently for our web search results. We care more about having the best possible results  because in the long run that’s what’s best for users and, therefore, our business.

Organizing information by indexing

The web is like an ever-growing public library with billions of books and no central filing system. Google essentially gathers the pages during the crawl process and then creates an index, so we know exactly how to look things up. Much like the index in the back of a book, the Google index includes information about words and their locations. When you search, at the most basic level, our algorithms look up your search terms in the index to find the appropriate pages.

The search process gets much more complex from there. When you search for “dogs” you don’t want a page with the word “dogs” on it hundreds of times. You probably want pictures, videos or a list of breeds. Google’s indexing systems note many different aspects of pages, such as when they were published, whether they contain pictures and videos, and much more. With the Knowledge Graph, we’re continuing to go beyond keyword matching to better understand the people, places and things you care about.