The search engine Google uses a method to provide ordered listings called Page Rank. Page Rank is fundamentally a concept of graph theory by using IP Addresses (your domain names address) as your vertices , and hyperlinks located on that site as edges.
In this form of graph theory, edges have weight. This means that the more weight for each edge, they are more likely to be traveled on if you think of the bridges example. In the case of search engines the higher weight accumulated for each website determines where it will be put in the order of search results.
What is interesting is that If a person knew exactly how the Page Rank algorithm worked then they could potentially have their website placed higher on google’s search results.
You can read more about it (Here on Cornell’s Blog)