Search Engine Ranking Explained
A search engine's goal is to generate a set of relevant, ranked results for every search query. Generating the search results is a two stage process. Initially, web pages which are relevant to the search term are extracted from the search engine's index. These results are then ranked based on each page's relevance to the search term. The results are presented in ranked 'relevance' order, with the most relevant page at the top of the results and the least relevant search terms at the bottom.
Search Term Subjectivity
The relevance of any given web page to a search term is subjective. Consider the search term SERPS. A high proportion of searchers will be looking for Search Engine Optimization information relating to the generation of Search Engine Results Pages (SERPs). However, the vast majority of searchers from the UK searching for SERPS will be expecting results relevant to State Earnings Related Pensions. In this example, the top ten ranking positions in Google are divided equally between pages relevant to pensions and those relevant to Search Engine Optimization.
Determining Relevance
Search engines gather information about web pages using software programs called robots, also known as spiders or crawlers. The information is broken down into snippets which are stored in a vast array of indexes maintained by the search engine. Google has stated that its algorithm (a mathematical formula used to determine relevance, and ultimately rankings) uses over 100 different factors in its ranking calculations. Factors include the text used in the H1 tag or the page's relationship with other pages. Each of the 100+ ranking factors has an associated weighting in the algorithm.
Generating Relevant Results
Search engine users want relevant results quickly. Google won’t calculate ranking positions for all of the millions of relevant pages but presents a maximum of 1,000 results for each search term. These 1,000 results are generated by performing algorithmic ranking calculations on a data set comprising 40,000 relevant pages drawn from Google's indexes. How the initial data set is drawn up depends on the number of relevant pages contained across the indexes. Having compiled the initial data set of 40,000 pages, these are ranked for relevance to the search term using all 100+ weighted ranking factors in the algorithm. The first 1,000 results are then presented, in ranked order, as the search results for the search term.
Search Engine Optimization
Search Engine Optimization requires the ability to 'reverse engineer' a web page so that it conforms to the search engine relevance model for a particular search term. Effective Search Engine Optimization therefore requires an understanding of the mechanisms and algorithms used by search engines to rank web pages. Since each search engine uses a different algorithm, and all the algorithms are continually being refined and adjusted, Search Engine Optimization is as much an experimental science as it is an art.
