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

To collect data from two websites with different URLs using a single Google Analytics property, cross-domain tracking must be set up. This feature allows Google Analytics to recognize users across multiple domains as they navigate from one site to another. Without it, sessions would appear to start anew with each domain, leading to fragmented data and an incomplete understanding of user behavior.

Cross-domain tracking involves modifying tracking code to ensure that session information and user IDs are maintained as visitors move between the different sites. This setup enables comprehensive reporting and analysis of user interactions across both websites, allowing for more robust insights into user journeys, traffic sources, and conversion paths.

The other options, while beneficial for specific tracking needs, do not facilitate data collection across multiple domains in the same direct way. Advanced filters are primarily used to segment or exclude data within a view in Google Analytics; event tracking focuses on specific user interactions on a page; custom dimensions serve to add additional variable data to reports but do not inherently connect data between different domains. Thus, cross-domain tracking is the essential feature for the scenario presented.