Relevance od Ad-Sense ads

How does google ad sense decide on what ads to display on your web pages ? I presume on page content however I have just added some ads to some property pages about specific countrys & it displays ads for totally irellevant countrys, does Google at a later date crawl the web page & display more relevant adverts than the ones it initially chooses to display when adding them to your webpage for the 1st time ?

Cheers.

It could be that they don't HAVE any ads available for the countries you mention on the page. So they do a "broad match".

PS: That happens more often if you use exotic ad shapes.

Ive noticed that different shapes give different results, in your experience which provide the most relevance ?

I find it quite bizzare that different shapes give different results, no logic...

There have been investigations into that:

http://www.jensense.com/archives/2005/07/top_three_ad_un.html

I'll take a look

I wanted to see the context in which Google viewed my blog so I cloned the page (I run it off my website) and added AdWords to it. The AdWords did not relate to my blog.

The first thing I changed was the title tag. No effect, same ads.
Next, I removed the meta tags. No effect, same ads.
Finally I removed all the copy. ...same ads.

Here I was with a blank page, no meta tags, no title tag and the same ads.

By my reckoning, the only way left by which Google could figure me out was the URL name. I changed it, reloaded the page and sure enough the ads related to the newly named URL.

Not sure why it ignored my content because I know that it does factor in on other sites. Perhaps because the page is new and has not been indexed or because it has no relevance based on IBLs.

Anyway, I am not an AdWords algo guru, just found it interesting.