User ID is a unique identifier assigned to individual users, letting you track their interactions across multiple sessions and devices in GoogleAnalytics 4 (GA4). Unlike the Client ID, which GA4 generates automatically and focuses on tracking anonymous sessions on a single device, the User ID gives you a more complete picture of a user's journey. This is super valuable for businesses looking to understand how users engage across different touchpoints, helping to refine marketing strategies and enhance user experiences.
Here’s the Lowdown on User ID in GA4
1. First off, the maximum length for a User ID you can send to GA4 is 256 Unicode characters. So, just keep that in mind when you're creating or assigning User IDs!
2. One thing to remember is that User IDs can’t be merged across different GA4 properties. If you want to track a single user’s journey, you need to stick with the same GA4 property throughout. This means if you manage multiple websites, you’ll have to funnel all that data into the same property to keep a consistent picture of the user's journey.
3. For effective tracking, it’s essential to send the User ID with every event when it’s available. Make sure to set the User ID field in your GA4 config tag so that all your event tags are in sync. The key here is consistency for accurate tracking.
4. Keep in mind that the User ID itself can’t be registered as a dimension in GA4. Also, avoid trying to register any other custom dimension (like crm_id) just to display the User ID in your reports. This can lead to high cardinality issues, which can mess with your data and throw off your reports.
If you work with GA4 to BigQuery exports, be sure to check out my SQL cheat sheet.
