1. A server-implemented method for search engine optimization, comprising: receiving (1) an identifier that identifies a domain, wherein a domain is a related collection of web pages, and wherein each web page comprises a plurality of web page elements, (2) a plurality of keywords for analysis relative to a search engine, where the search engine receives a keyword as input and generates as output search engine results pages that include a sequence of listings of web pages, wherein each listing corresponds to a web page and wherein each listing has a unique listing position and higher listing positions are more valuable than lower listing positions, (3) for each received keyword, a corresponding search volume that specifies the number of searches performed by the search engine for the received keyword over a defined period of time, and (4) for each received keyword, an average revenue per visit resulting from e-commerce transactions made by visitors to the identified domain, wherein said visits result from searches performed by the visitors using the received keyword; and for each received keyword: gathering search engine results pages from a search engine for the received keyword; determining listing positions for the received keyword in the identified domain from the gathered search engine results pages, wherein a listing position for a keyword in the identified domain is the position of a listing in the gathered search engine results pages whose corresponding web page is within the identified domain; selecting the highest listing position for the keyword in the identified domain from among the determined listing positions; mapping the received keyword to the web page that corresponds to the selected listing position in the identified domain; estimating, for each of the keywords mapped by said mapping to the designated web page, the revenue due to e-commerce transactions associated with the designated web page attributed to searches performed using the respective keyword, wherein said estimating is based on the corresponding search volume for each mapped keyword; limiting the number of keywords mapped by said mapping to a designated web page within the identified domain to a specified maximum value, wherein said limiting is based on the estimated revenue attributed to each of the keywords mapped by said mapping; and generating at least one instruction to modify a web page element in the web page that corresponds to the selected listing position.