In BigQuery, traffic attribution data is available at the user (first visit),
session, and event levels, corresponding to the different scopes used in
Google Analytics:

- **User-scoped:** Provides attribution for the user's first arrival. To determine first user traffic source, you can use the `traffic_source` dimensions associated with the `first_visit` event in the BigQuery export:
  - `traffic_source.source`
  - `traffic_source.medium`
  - `traffic_source.name`
- **Session-scoped:** Provides attribution for the source of each individual session. To determine session traffic source, use the `session_traffic_source_last_click` record. This record is available for every event and reflects the session-scoped last-click attribution data. Common fields include:
  - `session_traffic_source_last_click.manual_campaign.source`
  - `session_traffic_source_last_click.manual_campaign.medium`
  - `session_traffic_source_last_click.manual_campaign.campaign_name`
  - `session_traffic_source_last_click.google_ads_campaign.campaign_name`
- **Event-scoped:** Provides attribution for conversion events, using the cross-channel last-click attribution model. Every event in the BigQuery export has `traffic_source` populated. For conversion events, these fields contain the attribution data for that event:
  - `traffic_source.source`
  - `traffic_source.medium`
  - `traffic_source.name`

Use these fields to perform detailed attribution analysis within BigQuery and
join this data with other first-party datasets for enhanced insights.