Best Practices for Identifying Users

The most important calls you make with Segment are the Track and Identify calls. With the Track call, you can attribute actions on your site or app to individuals, and gain a better understanding of their activities, identity, and use patterns over time.

When you use the Segment Identify call with the Track call, you can start to build a complete picture of a user’s interactions with your systems, and help reduce the number of Monthly Tracked Users you are billed for.

AnonymousId generation

The Segment libraries generate an anonymousId for each user, even before you Identify them.

An anonymousId is a randomly generated 36 character string automatically assigned to a user on their first visit to your website or mobile application. You can use the anonymousId to link events performed by the user as they navigate around your website. When you track the anonymousId, you can attribute activities over multiple days to the same user by collecting all of the activities with that ID. If a user chooses to register for your site, or log in to your app, you can Identify them, and still include their anonymousId in the event payload along with the new userId.

Tip! Only the Segment mobile and website libraries automatically generate an anonymousId. If you use Segment’s Server libraries, you must generate an anonymousId manually. It can be any pseudo-unique identifier, for example you might use a sessionId from a backend server.

Identifying users

Segment’s Identify method lets you link a user to their actions and record traits about them. It includes a unique User ID, and records any traits you know about them, such as their email address, and name.

Segment recommends that you use a unique user identifier that won’t change for your userId, for example a database ID from your organization’s internal systems. (See below)

When you make an Identify call using Analytics.js, Segment saves the userId to the browser cookie, and writes all the user traits in local storage. If you’re using one of the Segment mobile libraries, the userId and traits are stored in the device’s memory. This makes it possible to append the user’s data to all subsequent Page calls or Track calls for the user, so you can properly attribute those actions.

If a user returns to your site after the cookie expires, Analytics.js looks for an old ID in the user’s localStorage, and if one is found, sets it as the user’s ID again in a new cookie. If the user clears their cookies and localStorage, all of the IDs are removed. The user gets a completely new anonymousId when they next visit the page.

Best options for userIds

A User ID should be a robust, static, unique identifier that you recognize a user by in your own systems. Because these IDs are consistent across a customer’s lifetime, you should include a User ID in Identify calls as often as you can.

Ideally, the User ID could be a database ID. For example, if you’re using MongoDB it might be a row identifier and look something like 507f191e810c19729de860ea. These can also be UUIDs that you generate somewhere in your application. You can also use identifiers that you get from other tools - such as Shopify or Braze - however this approach can lead to extra complexity in your systems.

Segment does not recommend using simple email addresses or usernames as a User ID, as these can change over time. Segment recommends that you use static IDs instead, so the IDs never change. When you use a static ID, you can still recognize the user in your analytics tools, even if the user changes their email address. And even better, you can link your analytics data with your own internal database.

Tip! Even if you don’t use an email address or a username as a User ID, you should still send them in the analytics payload as traits.

When to call Identify

You should make an Identify call in the following situations:

  • when first you create a user (and so it is assigned a userId)
  • when a user changes information in their profile
  • when a user logs in
  • Optionally, when you call Identify upon loading any pages that are accessible by a logged in user

Merging Identified and Anonymous user profiles

The illustration below shows a timeline with a user’s interactions on a website, including sample API calls above that show Segment calls, and the user’s anonymousId and userId.

When the user first visits a page, Analytics.js automatically assigns the user an anonymousId and saves it to the user’s local storage. As the user interacts with the site, for example clicking around to different pages, Analytics.js includes this anonymousId and some contextual information with each Page and Track call. The contextual information might be the user’s IP address, browser, and more.

When a user signs up to create an account on the website, the .identify(UID) and .track(“Signed Up”) events fire, in that order. You pull the userId unique to the user from your systems, and send it to the Segment library so you can label that user’s later events with their ID. The later Track call (“Signed Up”) contains both the userId and the automatically-collected anonymousId for the user, and any other information you capture about them - such as their first name, last name, and email address.

The example below shows an Identify call including user traits. It uses a database ID (97980cfea0067) as the userId.

analytics.identify("97980cfea0067", {
  name: "Peter Gibbons", //user trait
  email: "", //user trait
  plan: "premium" //user trait

For a Track call, information about this event is stored either in the context field or in the event properties. The example below shows a Track call including properties that tell you about the user.

analytics.track("Signed Up", {
  userId: "97980cfea0067", //event property
  name: "Peter Gibbons", //event property
  email: "", //event property
  plan: "premium" //event property

Additionally, Analytics.js adds a message_id and four timestamps to the call.

Now, as the user interacts with your site and different buttons or links that you track using Segment, their userId and anonymousId are sent with each tracking API call.

UserID merge examples

Let’s go through some more scenarios to explain how an anonymousId is assigned and how it might be merged with a UID.

Scenario #1 - Multi-day, single device

If a user clicks on an ad and is directed to a webpage, they are assigned an anonymousId. While this user is anonymous they navigate to different pages and click around on the website. Say they come back two days later from the same device, sign up, and are assigned a userId.

For simplicity, we’re assuming that the user has not cleared their cookies or localStorage, where the original anonymousId is stored. If they had, they’d be assigned a new anonymousId when they visited the website, and the userId they got when they register on the website would not be attached to the activities tracked with the old anonymousId.

Scenario #2 - Multi-day, multi-device, single login

In this scenario, the person uses both a web browser, and a mobile application to interact with your site. In each case, they are assigned a different anonymousId. In this scenario, the user signs up on the web browser, so Segment assigns their web session a userId. However, because they do not log in on the mobile application, Segment cannot tie the mobile activity to this specific user. Their mobile application activity remains anonymous unless they log in on the mobile application.

Scenario #3 - Multi-day, multi-device, multiple logins

Similar to the previous scenario, the user accessed both your website and mobile application, and also logged in on both. In this case, both sessions on the web and mobile app receive the user’s userId, so Segment can tie the anonymous activity on both web and mobile to this user.

User profiles in warehouses

Your data warehouse has a schema for each of your Segment sources. User information is stored in two tables in your source schemas - the identifies and users table.

The identifies table contains all of your identify events, and the timestamps for these events. Every time you make an Identify call, Segment adds the userId, anonymousId, any updated or added user traits from the call, as well as the timestamp of when the call was made. Your identifies table is your first stop when you have questions about users and their traits.

The users table contains only unique Identify method calls, and is a collation of the identifies table. The users table is the single source of truth for a user’s most up-to-date traits.

These tables only contain information about a user once they have been identified. However, you can still find information about an anonymous user on the pages, screens, and tracks tables, as well as the individual track event tables.

ID expiration and overwriting

The Segment ID cookie is set with a one year expiration. However, there are some ways an ID can be reset or overwritten:

  • If you call reset during a user’s browser session, it removes both their userId and anonymousId, which means the user generates a new anonymousId on the next visit.
  • If the user manually clears their cookies and local storage, they generate a new anonymousId on the next visit.
  • If you invoke any call before you set an anonymousId, Segment automatically sets the anonymousId first. This means if you explicitly set an anonymousId, you might give the user two anonymousIds or overwrite an existing one.
  • If you fetch the anonymousId using analytics.user().anonymousId() before one is set, Segment generates and sets an anonymousId rather than returning null.
  • If you call analytics.identify() with a userId that is different from the currently cached userId, this can overwrite the existing one and cause attribution problems.
  • If you generate a new anonymousId on a server library, and pass it from the server to the browser, this could overwrite the user’s existing anonymousId.

Remember, if a user has multiple devices, they can have different anonymousIds on each different device.

Linking server- and client- generated Ids

There are some advantages to sending details about your users directly from your server once the user registers. Server library Identify calls are invisible to the end user, making them more secure, and much more reliable.

If you want to send user data that is sensitive or which you don’t want to expose to the client, then you can make an Identify call from the server with all the traits you know about the user.

Aliasing from a server library

If you plan to track anonymous visitors from the browser and only make Identify calls from your server libraries, Kissmetrics and Mixpanel might require that you make an Alias call to link the records. The Alias call links client-side anonymous visitors with server-identified users. This isn’t recommended, but if you do this, read the Kissmetrics and Mixpanel specific alias docs.

Common questions

There are a few things that might cause your numbers to be off.

Missing sign-ups

The most common problem people run into when tracking new user signups client-side is that only a portion of their new users are showing up in reports.

This is usually caused by the page redirecting or reloading before the tracking calls get a chance to run. Segment recommends that you make those calls from a welcome page after the user registers, rather than trying to squeeze in the tracking calls on the sign-up page itself.

Anonymous history is lost

This is usually only an issue in Mixpanel, since it’s the only destination that requires a call to alias in the browser to link anonymous browsing history to a new identified user.

Remember that for destinations that require aliasing, you must make the Alias call before you make the Identify call for that user. Even if you make an Identify call from a server library, it can’t happen before the client-side alias.

This page was last modified: 25 Apr 2022

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