To collect data from two websites with different URLs using a single Google Analytics property, what feature must be set up?

Cross-domain tracking is essential when you need to collect data from multiple related websites (even with different URLs) into a single Google Analytics property. Without it, Google Analytics treats traffic between these sites as separate sessions and new users, leading to inaccurate user journey data and inflated user counts. Advanced filters are used to modify data views, not to combine data from different domains. Event tracking measures specific user interactions within a single domain or across domains once cross-domain tracking is set up. Custom Dimensions allow you to add custom data to hits, sessions, or users but don't facilitate tracking across different domains themselves.