Also known as Latent Semantic Analysis (LSA), this technology allows Google to analyze and quantify related keywords within the larger set of content on a webpage. Think word synonyms, different word endings, etc. Lots has been speculated about the extent that latent semantic indexing influences ranking.
It is a complex technology, particularly in how it may be implemented. The effect of LSI on your rankings is not well understood, but it means your page may rank better for a related keyword, one that may not even be on the page, than your primary keyword!
Following are the Places where keywords should be used:
The following are places where keywords should be used on your web pages. The first four items are more important, with Google giving weight to keywords found in the title and link anchor text more than any of the other locations.
Title: <TITLE>keywords</TITLE>. Keywords should appear as first or second word in the title.
Link (anchor) text: <A HREF>keywords</A>. The clickable portion of links.
Headings: <H1>keywords</H1>, <H2>keywords</H2>, etc. Use a stylesheet (CSS file) to control the size of heading text to make it blend in better.
First paragraph of page (first 20 words): <BODY><P>keywords</P> Bold and/or italicize keywords also.
Last paragraph of page: <P>keywords </P></BODY>
Drop-down boxes: <FORM><OPTION>keywords</OPTION></FORM>
URLs: <A HREF=”http://www.keywords.com/”></A>
Folder & file names: keywords/keywords.html, keywords.gif
Image ALT text: <IMG SRC=” ” ALT=”keywords” > for graphical links
Some people abuse H1 tags by wrapping them around entire pages of content or by using multiple H1 tags on a page.
This is a bad idea and borders on spam – the H1 tag should be used as a page headline. It is perfectly legitimate to reduce the size of H1 text using a style sheet but that’s about it. As a result, Google may be discounting H1 so it may carry less weight for ranking moving forward.
The same can be said about image ALT text – some people put entire paragraphs of content in them for each image on a page. It is perfectly legitimate to put keywords relating to the image but that’s it. Similarly, image ALT text now carries less weight than before. Images that are clickable (wrapped in a HREF link tag) do not appear to have a discounting – yet.