Google Search Engine Backlink Factors and Value of dofollow Backlinks 1 - Linking Domain Age: Links from aged domain many be more powerful than new domains. 2 - Number of Linking Root Domains: The number of referring domains is one of the most important ranking factors in Google's algorithm. 3 - Number of Links from Separate C-Class IPS: Links from separate class-c IP addresses suggest a wider breadth of sites linking to you. 4 - Number of Linking Page: The total number of linking pages, even if some are on the same domain. 5 - Links from .edu or .gov Domains: Matt Cutts has stated that TLD doesn't factor into a site's importance. However, that doesn't stop SEOs from thinking that there is a special place in the algorithm for .edu and .gov TLDs. 6 - ALT Tag (for image links): Alt text is an image's version of anchor text. 7 - PageRank of Linking Page: The PageRank of the referring (linking) page is an extremely important ranking factor.