Complete GA4 Migration Guide

With Universal Analytics no longer processing data, organizations must fully transition to Google Analytics 4 (GA4). This comprehensive guide covers everything you need to know about migrating to GA4, from data model differences to implementation strategies and historical data preservation.

Understanding the GA4 Data Model

GA4 represents a fundamental shift in how Google Analytics collects and processes data. Understanding these differences is crucial for a successful migration.

UA vs. GA4: Key Differences

Aspect	Universal Analytics	GA4
Data Model	Sessions & Pageviews	Events & Parameters
User Identity	Client ID	User ID + Device ID
Custom Dimensions	20 (Standard) / 200 (360)	50 Event / 25 User
Goals/Conversions	20 Goals per View	30 Conversions per Property
Views/Data Streams	Multiple Views	Data Streams

Event-Based Data Model

Everything in GA4 is an event, including pageviews:

page_view - Pageview (automatically collected)
session_start - New session begins
first_visit - First visit by user
scroll - 90% page scroll (enhanced measurement)
click - Outbound link click (enhanced measurement)
purchase - E-commerce transaction (recommended event)

Event Categories in GA4

Automatically Collected: page_view, session_start, first_visit, user_engagement
Enhanced Measurement: scroll, outbound_click, site_search, video_engagement, file_download
Recommended: login, sign_up, purchase, add_to_cart (use Google's names)
Custom: Any business-specific events you define

Migration Planning

Step 1: Audit Current UA Implementation

Document everything in your current Universal Analytics setup:

All custom dimensions and their values
Custom metrics
Goals and goal values
E-commerce tracking setup
Events (Category/Action/Label structure)
Filters applied to views
Custom reports and dashboards
Integration with other tools (Google Ads, Search Console)

Step 2: Map UA to GA4

Create a mapping document translating UA concepts to GA4:

// UA Event Structure
Category: "Video"
Action: "Play"
Label: "Product Demo Video"

// GA4 Equivalent
Event Name: "video_start"
Parameters:
  - video_title: "Product Demo Video"
  - video_provider: "YouTube"
  - video_url: "https://..."

Step 3: Plan Custom Dimensions

GA4 has different scope options:

Event-scoped: Attached to specific events (50 available)
User-scoped: Persist across all user's events (25 available)

Map your UA custom dimensions:

// UA Custom Dimensions
CD1: User Type (User scope) → GA4 User Property
CD2: Page Category (Hit scope) → GA4 Event Parameter
CD3: Author Name (Hit scope) → GA4 Event Parameter
CD4: Login Status (Session scope) → GA4 User Property

Implementation Methods

Method 1: Google Tag Manager (Recommended)

GTM provides the most flexibility for migration:

Create GA4 Configuration Tag

// GA4 Configuration Tag Settings
Tag Type: Google Analytics: GA4 Configuration
Measurement ID: G-XXXXXXXXXX
Fields to Set:
  - send_page_view: true
  - debug_mode: true (during testing)

Create GA4 Event Tags

For each custom event, create a GA4 Event tag:

// GA4 Event Tag Example
Tag Type: Google Analytics: GA4 Event
Configuration Tag: {{GA4 Config}}
Event Name: form_submit
Event Parameters:
  - form_name: {{DLV - Form Name}}
  - form_location: {{DLV - Form Location}}

Method 2: gtag.js Direct Implementation

For sites without GTM:

<!-- Google tag (gtag.js) -->
<script async src="https://www.googletagmanager.com/gtag/js?id=G-XXXXXXXXXX"></script>
<script>
  window.dataLayer = window.dataLayer || [];
  function gtag(){dataLayer.push(arguments);}
  gtag('js', new Date());
  gtag('config', 'G-XXXXXXXXXX');
</script>

<!-- Track Custom Event -->
<script>
  gtag('event', 'form_submit', {
    'form_name': 'Contact Form',
    'form_location': 'Footer'
  });
</script>

E-commerce Migration

GA4 uses a different e-commerce data layer structure:

Product View (UA vs GA4)

// Universal Analytics Enhanced Ecommerce
dataLayer.push({
  'ecommerce': {
    'detail': {
      'products': [{
        'name': 'Product Name',
        'id': 'SKU123',
        'price': '29.99',
        'brand': 'Brand Name',
        'category': 'Category'
      }]
    }
  }
});

// GA4 E-commerce
dataLayer.push({ ecommerce: null }); // Clear previous
dataLayer.push({
  'event': 'view_item',
  'ecommerce': {
    'items': [{
      'item_id': 'SKU123',
      'item_name': 'Product Name',
      'price': 29.99,
      'item_brand': 'Brand Name',
      'item_category': 'Category'
    }]
  }
});

Purchase Event

dataLayer.push({ ecommerce: null });
dataLayer.push({
  'event': 'purchase',
  'ecommerce': {
    'transaction_id': 'T12345',
    'value': 99.98,
    'currency': 'USD',
    'tax': 5.00,
    'shipping': 10.00,
    'items': [{
      'item_id': 'SKU123',
      'item_name': 'Product Name',
      'price': 29.99,
      'quantity': 2
    }]
  }
});

E-commerce Parameter Changes

GA4 uses different parameter names: id → item_id, name → item_name, category → item_category. Update your data layer accordingly.

Historical Data Preservation

GA4 does not import historical UA data. Preserve your data using these methods:

Option 1: Export to BigQuery

Enable BigQuery linking in UA (360 only)
Export daily tables before UA shutdown
Link GA4 to BigQuery for continuity

Option 2: Google Analytics API Export

Use Reporting API to extract key metrics
Store in data warehouse (BigQuery, Snowflake)
Create combined dashboards

Option 3: Third-Party Tools

Supermetrics for scheduled exports
Data Studio connectors
Analytics Canvas for bulk export

Configuration and Settings

Data Streams

Configure separate streams for:

Web (your website)
iOS app
Android app

Enhanced Measurement

Enable these automatic tracking features:

Scrolls (90% threshold)
Outbound clicks
Site search (configure query parameter)
Video engagement (YouTube embeds)
File downloads

Conversions

Mark important events as conversions:

Navigate to Admin → Events
Toggle "Mark as conversion" for key events
Maximum 30 conversions per property

Testing and Validation

Debug Mode

Use GA4 DebugView for real-time validation:

Install GA Debugger Chrome extension
Enable debug mode in GTM or gtag
Navigate to Admin → DebugView
Verify events and parameters in real-time

Validation Checklist

All pageviews tracking correctly
Custom events firing with correct parameters
E-commerce events capturing transaction data
User properties persisting across sessions
Conversions recording properly
Cross-domain tracking working (if applicable)

Reporting Differences

New Reports in GA4

Exploration: Build custom reports with drag-and-drop
Path Analysis: Visual user journey flows
Funnel Analysis: Conversion funnel visualization
Segment Overlap: Compare audience segments

Missing Reports

Some UA reports don't exist in GA4:

Bounce Rate (replaced by Engagement Rate)
Goals (replaced by Conversions)
Site Speed (use Core Web Vitals instead)

Conclusion

Migrating to GA4 requires thoughtful planning and execution, but it's also an opportunity to improve your analytics foundation. The event-based model provides more flexibility, and features like BigQuery export unlock powerful analysis capabilities. Take time to properly map your requirements, test thoroughly, and train your team on the new interface.

Need help with your GA4 migration? Contact WegWorks for expert analytics implementation services.