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ID mapping connects different identifiers to the same user, enabling cross-device targeting, measurement, and analytics. When a data provider links a hashed email to a mobile advertising ID, or a cookie to a device identifier, they create an ID mapping that bridges previously siloed data.

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Why ID mapping matters

Modern consumers interact with brands across multiple touchpoints:
  • Mobile apps (identified by MAID)
  • Websites on desktop (identified by cookies)
  • Email communications (identified by email address)
  • Connected TV (identified by device graphs)
Without ID mapping, each touchpoint exists in isolation. A retailer might show the same ad to a customer on mobile, desktop, and CTV without recognizing it’s the same person—wasting budget and creating a poor experience. ID mapping solves this by creating links between identifiers, enabling:
  • Unified targeting: Reach the same person across devices
  • Frequency capping: Limit ad exposure across channels
  • Attribution: Connect conversions to the right touchpoints
  • Audience expansion: Find customers in new channels

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Common ID linkages

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Hashed Email to MAID

The most valuable and deterministic mapping connects hashed emails to mobile advertising IDs. How it works: When a user logs into a mobile app with their email address, the app developer can link the MAID (from the device) to the hashed email (from the login). This creates a deterministic, high-confidence link. Use cases:
  • Target email subscribers in mobile apps
  • Extend CRM audiences to mobile advertising
  • Measure mobile conversions against email campaigns
Connects web browsing behavior to mobile device identity. How it works:
  • Cookie syncing through pixel fires on mobile web
  • SDK-based matching when users interact on both web and app
  • Probabilistic matching based on shared signals (IP, location, behavior)
Use cases:
  • Retarget website visitors in mobile apps
  • Build unified user profiles across web and app
  • Measure cross-platform campaign performance
Links browser-based identity to email-based identity. How it works: When users log in on websites, the site can link their cookie to their hashed email. This creates a durable identifier that persists even when cookies are cleared. Use cases:
  • Build persistent identity across browser sessions
  • Connect anonymous browsing to known customers
  • Enable email-based audience activation

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ID mapping quality

Not all ID mappings are equal. Consider these quality factors:

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Deterministic vs. probabilistic

Deterministic mappings are more accurate but harder to scale. Probabilistic mappings offer broader reach but may include false matches.

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Recency

ID mappings can become stale:
  • Users reset their MAIDs
  • Cookies expire or are cleared
  • Email addresses change
More recent mappings are generally more reliable.

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Source quality

The method of collection matters:
  • First-party login data: Highest quality
  • SDK integrations: High quality
  • Cookie syncing: Medium quality
  • Probabilistic inference: Variable quality

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ID mapping in Narrative

Narrative enables ID mapping through several mechanisms:

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Standardized identifiers

When ingesting data, Narrative normalizes identifier formats to enable matching across sources:
  • Consistent casing for MAIDs
  • Standardized hashing for emails and phones
  • Narrative Cookie IDs for cross-supplier cookie matching

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Cross-supplier matching

Different data suppliers use different cookie namespaces. Narrative creates a standardized cookie ID that links to each supplier’s cookies, enabling matching across suppliers.

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Query-time joining

Use NQL to join datasets on shared identifiers:

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Privacy considerations

ID mapping must respect privacy regulations and user expectations:
  • Consent: Ensure mappings are created with appropriate user consent
  • Pseudonymization: Always hash PII before creating mappings
  • Data minimization: Only create mappings needed for specific use cases
  • User controls: Honor opt-outs across all linked identifiers

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Related content

Identifier Types

Categories of identifiers used in mapping

Data Onboarding

Connect offline data to online identifiers

UID2

Privacy-preserving universal identifier

Narrative ID

Secure cross-partner matching