How do search engines list and rank sites?
Each search engine and directory has its own set of Web page ranking and listing criteria. Generally, search engines utilize proprietary ranking algorithms to determine the quality and relevance of a visited Web page. Based on that assessment, the search engine will decide whether or not to add the page in question to its index.
When calculating page rankings, search engines focus on Web page elements such as page copy, Title tags, keyword usage, and the abundance and relevance of inbound hyperlinks. The latter issue is a particularly prominent element of Google's ranking algorithm.
Most search engines use spidering technology to collect the listings for their indices. Web directories generally rely on human editors, and page inclusion and ranking decisions are in the hands of those editors. The editors decide if a suggested URL will be included in the directory, and if so, which category and subcategory. Most directories present their listings alphabetically.