Difference between rel="canonical" and og:url?
I'm having trouble understanding canonical URLs with regards to how search engines and Facebook seem to handle them.
My Google maps powered site allows visitors to use social media to request a gig in their country. One of the pages in question can be found at: http://izzy.nogig.in/
When a user clicks on their countries marker it gives them sharing options (twitter/facebook/etc), which when shared will share the URL specifically for that country, eg: izzy.nogig.in/usa? or izzy.nogig.in/spain? etc.
All of these countries in the URL amount to a lot of duplicate content so I use the following to point search engines to the page I want ranked:-
<link rel="canonical" href="http://izzy.nogig.in/_?"/>
For Facebook Likes to count towards each individual country I've set my Open Graph "og:url" as follows, eg:
<meta property="og:url" content="http://izzy.nogig.in/australia?" />
Now when I run a country-specific URL through the Facebook Object Debugger (eg. http://developers.facebook.com/tools/debug/og/object?q=http%3A%2F%2Fizzy.nogig.in%2Faustralia%3F) it shows the following:-
Response Code: 206
Fetched URL: http://izzy.nogig.in/australia
Canonical URL: http://izzy.nogig.in/australia
Mismatch og:url and canonical url:
og:url tag in the header is not the same URL as rel='canonical' link in the html.
The above error is what's confusing me. I know they're mismatched, but I thought this was the correct way to do this.
Everything in the debugger looks good to me (correct link, description, image etc for each country), and I can't change the rel="canonical" value to match my og:url as I need it pointing to a single page (country-less) for search engines.
I believe it is all working correctly. Should I just ignore the error from the debugger, or have I set this up incorrectly? I don't want "likes" for each country all disappearing and counting towards the rel="canonical" URL.
Many Thanks - Will
Answer
link rel="canonical" will be used by search engines where as og:url will be used by facebook
og:url basically tells the FB scraper "ignore anything on this page, and scrape this url instead"
More for Canonical link element: http://en.wikipedia.org/wiki/Canonical_link_element