To learn more about domain names, visit: Moz.com/learn/seo/domain.
On that page, Moz defines "subdomains" as follows:
Subdomains are the third level of a domain's hierarchy and are parts of a larger top-level domain. They are added in front of the root domain and separated from the domain name with a period.
For example, "blog.example.com" and "english.example.com" are both subdomains of the "example.com" root domain. Subdomains are free to create under any root domain that a webmaster controls.
Many multi-campus churches prefer to have their campus websites on subdomains like "city.church.com" to maintain the branding of the church network along with the location. While this does provide a visual connection to the church branding, it may not be helpful for ranking on Google.
For years Google has maintained that it ranks domains and subdomains the same. However, many SEO leaders have found that when you move a subdomain from "city.church.com" to an internal page like "church.com/city"—it almost always increases search engine traffic. Some people even found that their traffic doubled overnight. And the opposite is also true. When you move an internal page like "church.com/city" out to a subdomain like "city.church.com"—it almost always decreases search engine traffic. With some people finding that after their traffic declined, it did not recover even after 6 months.
Something else to take note of, although Google (the company) often uses subdomains for many of their website services (like "analytics.google.com" and "mail.google.com"). The Google Maps website which used to be at "maps.google.com" is now at "google.com/maps" (a significant change, given how Google ranks Google Maps in its search results).
With that said, there are many factors that may be involved in these verifiable increases and decreases in traffic. And one of the biggest key reasons may have nothing to do with the "domain vs. subdomain" debate. Since Google maintains that it ranks domains and subdomains the same, it may be a content issue and not a domain issue which leads to an increase or decrease in traffic to the website.
Google LOVES content that matches the intent of the search. When content more closely matches the search query, the better that content will do on Google. And within the context of a multi-campus ministry, if Google finds multiple pages about different campus locations all on the same website, that single site will have more authority and rank higher. However, if you split up that same content up across multiple campus websites, the individual "child" websites will not be as authoritative as the "parent" website if all the content is combined.
A few years ago, Rand Fishkin, Founder and former Wizard of Moz, said the following:
I would still strongly urge folks to keep all content on a single subdomain. We recently were able to test this using a subdomain on Moz itself (when moving our beginner's guide to SEO from guides.moz.com to the current URL moz.com/beginners-guide-to-seo). The results were astounding—rankings rose dramatically across the board for every keyword we tracked to the pages. I've had the opportunity to see many dozens of other sites do the same, almost always with similarly positive results...
We still... have overwhelming evidence that Google doesn't consistently treat all pages on multiple subdomains the same way they do URLs on the same subdomain. They've said for years that it doesn't matter, but the evidence and data are clear. Putting content on multiple subdomains will almost certainly cause it to perform worse in Google than keeping it all on the same subdomain.
And more recently he shared the following via Twitter:
- Moving subdomain → subfolder (almost always) increases search traffic
- Moving subfolder → subdomain (almost always) decreases search traffic
As mentioned above, the subdomain is what comes before your domain (city.church.com), and subfolders are the pages that come after your domain (church.com/city). Considering that the statements above are backed up by years of proven research and case studies across multiple websites in the USA and the UK, churches should take note.
With that said, if a subdomain is mission-critical for your multi-campus ministry, no worries. As long as you can build enough unique content on each subdomain site that matches what people are searching for on Google, then please do what will serve your mission to reach people for Jesus. Just be aware that you will need to invest a considerable amount of effort into building different pages, sermon transcripts, event content, and blog posts with as much helpful content as possible in each campus website.