How to: Boost metadata in SharePoint search results

As pointed out by Mike Fairly in the TechNet forums (see thread), the default rank profile, or any other rank profile included with SharePoint, does not give any weight in particular to tagged content.

This means that if you add managed metadata columns or Enterprise Keywords to a list or library, the terms used will merely help on content recall, but not provide any extra rank to the items moving them higher up in the search results.

On the other hand, when promoting the use of tagging to information workers, you might think they want a return on investment for those tags, meaning tagged items should appear higher in the result set.

There are several ways to go about fixing this:

1. Create a custom rank profile
2. Change the weight of managed properties
3. Use dynamic ranking via the XRANK operator

The easiest in terms of implementation and flexibility is #2.

Rank models in 2013–Main differences from 2010

Disclaimer: I’m by no means a math expert and my statements below might not be 100% accurate, but I try my best. Also, be careful when tuning the rank profile as changing numbers can have a big effect on your ranking.

With the new FAST search core, ranking has changed quite a lot from 2010. Newly published content on MSDN explains a bit more how rank is calculated and how you can change it.
As the O14 rank model is available in SharePoint 2013 (O15), I will try to outline some of the major differences you can expect to see regarding how results are ranked/sorted by default.
You can pull out the rank model xml yourself from both models using PowerShell.

$ssa = Get-SPEnterpriseSearchServiceApplication
$owner = Get-SPenterpriseSearchOwner -Level ssa

$o15 = Get-SPEnterpriseSearchRankingModel -SearchApplication $ssa -Owner $owner -Identity 8f6fd0bc-06f9-43cf-bbab-08c377e083f4
$o15.RankingModelXML > o15.xml

$o14 = Get-SPEnterpriseSearchRankingModel -SearchApplication $ssa -Owner $owner -Identity 9399df62-f089-4033-bdc5-a7ea22936e8e
$o14.RankingModelXML > o14.xml

Then it’s all a matter of comparing the models.