What does a spatial reference define in ArcGIS Online?

A spatial reference in ArcGIS Online defines both the coordinate system and the projection used for spatial data. The coordinate system establishes how data is measured and represented on the Earth's surface, allowing for accurate positioning of maps and geographical features. It determines the framework for the data's spatial relationships, which is crucial for analysis and visualization.

The projection refers to the method by which the three-dimensional surface of the earth is represented on a two-dimensional plane, such as a map. Different projections can preserve certain properties like area, shape, or distance, depending on the needs of the map or analysis being conducted. The correct definition of spatial reference underscores its importance in ensuring that various data layers align correctly and function together within a mapping environment.

In contrast, the other choices pertain to different aspects of data and mapping. While the style of the map refers to the aesthetic design and visualization aspects, and the data format involves how data is stored and structured, access permissions relate to the security and management of data rather than its geographical representation. Understanding the role of spatial reference is crucial for anyone working with geographic information systems, as it forms the foundation for accurate spatial analysis and mapping.