Items such as CSV files, shapefiles, and map notes can be added to a map as feature collections. A feature collection is a type of feature layer. Any feature collection you add can be saved as part of the map. You can also save a feature collection as its own item by clicking Save Layer in the layer properties menu. The item will appear as a new feature collection item in My Content and can be shared with others and added to multiple maps.
When you save a feature collection as part of a map, the data is saved as part of the map. Any changes you make to the feature collection, for example, by editing data, are only reflected in the map. The changes are not applied to the original CSV file, shapefile, or map note from which the feature collection was derived.
When you save a feature collection as its own item, the data is retained with the feature collection item and not stored as part of the map. Any changes you make to the feature collection item, such as modifying its data, are saved once you click Save Layer. If the feature collection item is used in other maps, the changes will be reflected there as well. If the feature collection item is deleted from My Content, it will no longer be available to others.