Before we get into the setup and results of the test, I think it’s important to quickly explore what the CID URL actually is and what those strings of numbers represent, as well as why they are so important to your GMB listing.

CID stands for Cluster Document Identifier. The act of clustering your documents during information retrieval allows a database to quickly reference an entire corpus or set of pages using only a unique numerical identifier. What this means is, as Google’s engine is out discovering new mentions for your entity (these new mentions ARE your documents), the engine is also assigning these documents to a particular local entity via the cluster document identifier. These documents help make up part of the local ranking factor and the CID URL is a direct representation of your entity in the local search engine and the entire collection of documents (and the weight of those documents) for the entity.

Because part of the cluster document process involves selecting and assigning credit to the correct entity for each discovered document, we can see how the concept of linking to that URL within a document could make it easier for the local engine to assign the document to the correct entity. And yes, this is actually a very serious issue, as well as being the entire reason people preach about the importance of clean data and a consistent NAP for local SEO! If Google is confused as to which entity to assign a document to (aka a citation or brand profile), you might not get credit, nor any corresponding ranking boost from that document.

If you want to start link building to your GMB CID URL, check out this short three-minute video detailing three quick methods of finding your CID URL.