Who knows how to check and understand how Google sees the 'relevancy'; The basic thing is just the same topic, but what about related topics, say Dog and Cat both are animals? Paris and Londong both are places (cities) Computers and Internet and Internet Marketing = can't exist without each other? But how Google determinates it?
You are talking about Semantics there, and yes it is possible to run this fully but it take an awfyl lot of processing power. Another thing you see is the fact it is language based, and to get it to work you need to use LSI (latent Semantic Indexing). This works in such a way that a generic word like 'windows' can be put into the context of the page. EG windows are great to see through windows is a computer operating system. Now are those two pages related because they are both about windows? NO of course not. LSI however can look at the words and put them into context EG windows= operating system= OS = Linux = computer programme etc So if you search for Windows, it might return pages about computer operating systems. That said, Google prefer going down the Social Networking side of things in their algorithm. Google prefers to say that topics are related if the social networking structure says they are. EG you use dog & cat as an example, and yes they are sort of related, but by your premise so is rabbit, reptiles, fish amphibians etc how to decide which is MOST relevant to each other? You have two options, social networking (linking structure and relation of links between the pages) and full blow LSI. Currently full blown LSI is out of the question because of resources, so what the SE's do is to use 'clustering technology' to build social network clusters, which by the very nature of social networking will be on topic and also cover related topics in their links. That really is a heavy start to a Saturday morning LOL. Ask me a question about rugby I am much lighter on that
There a site called google sets labs.google.com/sets. Put in some keywords and it will give out some related keywords. It might be a good place to start with relevancy.
Try this tool ... it'll show you how Google sees your site: http://www.digitalpoint.com/tools/adsense-sandbox/
The google ads tool can only show you relevant ads if people are bidding on your topic, AND google can work out what your page is about.
No big difdference. Same topic and related topics are no different when doing directory submissions, link exchanges, etc.
Great post by Old Welsh Guy. He hit it on the head. This is a very tricky subject as it pertains to semantics and part of google's algorithm which nobody really knows all the secrets to. But I was going to say, its all about figuring out close relatives of keywords to simplify it for SEO. So in your example, dogs aren't related to cats, Paris isn't related to London and computers aren't really related to the internet. In terms of SEO if you are looking for related sites to get links from just look for ones that have the same overall subject. I'll stick with the topic of Dogs. Get links or link out to sites related to dog collars, dog tricks, dog food etc. Also, if you have a dog site google is not going to penalize you if you link out to a site about cats, but they might if you link out to casinos. Staying under the same topic is pretty much safe.
looks nice in theory, but i wonder why google thinks my page is related to porn? (had a referer for a related:somepornsite.com a few weeks ago)
I think yu missed what I posted Google does not currently use that system fully, it chooses to go down the social networking route of linking clusters. If Google thinks your site is related to prn sites, then you might well have drawn yourself into a bad neighbourhood