Google Webmaster: What is the point of adding www and non-www properties?

Question

I just start using Google Webmasters tool. When I add a domain with or without www, there will be a message from google saying I need to add the other to improve the 'exposure'. If I do this, there will be two properties (with and without www), which are basically the same website. Then Google instructs me to set a preferred one. My questions are:

1. Why can't these two properties be merged into one?
2. I take it that after I set a preference, the data of the two properties will be identical, won't it?
3. If I didn't set the preference, will people typing example.com not be counted as the traffic of www.example.com?

Answer 1

1. Why can't these two properties be merged into one?

Technically, http://www.example.com is not an alias of http://example.com or vice-versa. You can show completely different things on www and non-www versions. However, most websites use them interchangeably and webmasters prefer one over the other and based on their preference (different reasons - use of cookies is one of them), redirect requests for one to the other.

It is also recommended thing to do, select one version www or non-www and redirect the other one to the selected version. This way, you will have one version of truth and not worry about different effects of having two versions such as SEO, analytics tracking, etc.

If you use htaccess, you can use the following code -

For www to non-www version.

RewriteCond %{HTTP_HOST} ^www\.example\.com [NC]
RewriteRule ^(.*)$ http://example.com/$1 [L,R=301]

For non-www to www version -

RewriteCond %{HTTP_HOST} ^example.com$
RewriteRule (.*) http://www.example.com/$1 [R=301,L] 

or search on internet for other ways to do this.

2. I take it that after I set a preference, the data of the two properties will be identical, won't it?

I think google asks for the preference as to what they should show in the search results. www or non-www version. It is not necessary to set this preference if you are using redirection and have only one version of internal links on the website, crawlers will see only your preferred version.

I am not sure, how you have 2 properties in WMT. However, if you are using redirection, all data will be for one version.

3. If I didn't set the preference, will people typing example.com not be counted as the traffic of www.example.com?

Again, use redirection to avoid such a scenario. People who are typing in example.com should be redirected to www.example.com and tracking will now be alright. Preference settings in WMT won't help here at all.

Answer 2

The simple answer why Google recommends this practice is that:

When you consolidate to either www or non www via ht access + WMT

Your Google rankings for your keywords will rank higher.

Why? Because you would have external links to www or non www

And now all the link juice from either www or non www is routed to 1 of the 2 instead of separated to both.

Thus increasing your rankings.