ISEdb.COM

What is the difference between a
sub-domain and a sub-directory? In the electronic eyes of GoogleBot,
not much though one is easier for the bot to deal with and the other is
(in certain circumstances), easier for a webmaster to deal with.

A sub-domain prefixes the domain-name at the host level as such: ppcassurance.metamend.com. A sub-directory is a set of files that are seen as a suffix to the domain-name such as, metamend.com/blog.

Up until a couple of months ago, a general piece of SEO advice was
to separate distinct topics addressed under the same URL to
sub-domains. This was done to help search-spiders differentiate between
topics and also so search-spiders would treat the information at a
sub-domain as they might a unique website. Using sub-domains, SEOs
could conceivably capture a far larger number of Top10 placements under
the same keyword phrases for different parts of the same company. In
that way, SEOs could offer five or six (or more) of ten first page
placements as opposed to the more frequent two front page placements
under the same phrase.

Last week at WebmasterWorld’s PubCon show in Las Vegas, Google’s Matt Cutts explained to WepProNews
some changes Google has made to its algorithm to decrease the number of
listings from the same domain being displayed on the first page in
Google results. In most cases, Google no longer differentiates between
sub-domains and sub-directories though it continues recognize
differences in topic between main-domain and sub-domains in certain
situations.

In a post-PubCon blog post, Matt
notes that it is far easier for Googlebot to detect and spider files
contained in a sub-directory. It is also far easier for webmasters to
set up a site using the traditional sub-directory structure. This is
what Googlebot was designed to do and, with far fewer assumptions to
make about topical relevance between URLs, the sub-directory structure
is simplest for search engines.

For highly adventurous webmasters however, using sub-domains
conveyed a possibly unfair advantage when chasing a larger share of the
first page of search results. A cool SEO trick was to assign
sub-domains to different host servers spread around the country or
world. That way, Google would not detect and associated the same IP
numbers from the host-server. The idea was to make Googlebot think it
was looking at a unique website while still associating strong
placements gained at the domain and sub-domain with each other. For
almost three years, effective use of sub-domains was a well used
“secret” tactic.

According to Matt’s post,

“For several years Google has used something called “host crowding,”
which means that Google will show up to two results from each
hostname/subdomain of a domain name. That approach works very well to
show 1-2 results from a subdomain, but we did hear complaints that for
some types of searches (e.g. esoteric or long-tail searches), Google
could return a search page with lots of results all from one domain. In
the last few weeks we changed our algorithms to make that less likely
to happen.”

Interestingly, Matt reports the change in the algorithm occurred at
least a few weeks ago. There has been little talk of the alteration in
SEO discussion forums or social networks, indicating that most SEOs
haven’t noticed. The topic was addressed because someone “…asked his
advice on sub-domains vs. sub-directories.”

Matt Cutts’ post on sub-domains vs. sub-directories is well worth the read as are the 96 (or so) comments that follow the post.

Some made by extremely well known SEOs ask questions about
sub-domains and unique circumstances such as languages (ie:
fr.example.com or de.example.com).

For instance,

Kalena Jordan asked,
“What about sites that target different regional markets? Does it still
make sense for them to use sub-domains e.g. australia.site.com,
uk.site.com and use the new Regional Association tool in Webmaster
Tools to indicate which searcher region each sub-domain should be
associated with?”

To which Matt replied.
“Kalena, using subdomains for stuff like fr.example.com or
de.example.com is still a great approach, because those sites may be
similar in idea, but the language is usually completely different.”

Matt’s answer gives a great clue into what Google wants to see at
sub-domains vs. what they would prefer to see in a sub-directory. There
are cases where the size of a site dictates the approach a webmaster
would wish to take. Large networks that create unique content for
different cities might be better served using sub-domains
(vancouver.example.com/, seattle.example.com/, nyc.example.com), if
information varies from city to city while sticking to a similar
topical format. (ie: tourist accommodation, local search, blue widget
factories, etc…)

The artful tactic of sub-domaining has likely lost a bit of the
power it used to hold however many SEOs say they will continue the
practice as it suits their research and deployment techniques.

In our own unending pursuit of quasi-scientific SEO research, we are
taking a harder look at how we use sub-domains with an eye to improving
SEO outcomes for ourselves and our clients. The traditional 4-week lull
around the end of the year is a perfect time to post and evaluate
experimental site structures, just to see what happens. If we see
interesting results, we’ll post them to this space next year.