How can layers be configured in ArcGIS Online?

Configuring layers in ArcGIS Online involves various customizable features that enhance the visualization and interactivity of geospatial data. Adjusting visibility ranges allows users to control which layers are displayed based on zoom levels, ensuring that the map is not cluttered with unnecessary information at certain scales. Symbology can be modified to represent different data categories or to emphasize specific attributes visually, making it easier for users to interpret the information. Additionally, pop-ups can be configured to provide relevant data and context when users click on a feature on the map, improving the user experience and data interaction.

The other options focus on limited or inaccurate aspects of layer configuration. Creating links to external databases is a specific action that may complement layer use but does not define configuration. Layering only raster data is overly restrictive, as ArcGIS Online supports both vector and raster data formats for comprehensive mapping solutions. Standardizing all attributes to one format is not a necessary condition for configuring layers, as different attributes can coexist and be represented without needing to conform to a single format.