A basemap layer is a special type of group layer that is drawn using optimized map display logic and utilizes a local cache to refresh the map quickly. Basemap layers also help reduce network traffic since ArcMap does not need to contact the server repeatedly to retrieve the map extent. Basemap layers can contain any layer format, such as feature classes, shapefiles, web services, or rasters. If you place feature layers in the basemap, you can snap to their features while editing, measuring, georeferencing, and using other tools that work with the Snapping toolbar.
For example, if you edit data for a water district, your operational layers, such as manholes, water main lines, and valves, cannot be part of a basemap layer because you cannot edit layers inside a basemap. However, you could include a land base of parcel boundaries, buildings, streets, and other built features that you are not editing inside a basemap layer to improve performance. When creating a new waterline, you can still snap to the parcels even though it is inside the basemap.
- Ensure snapping is enabled. On the Snapping toolbar, click the Snapping menu and make sure Use Snapping is checked.
- Click the Snapping menu on the Snapping toolbar and click Options.
- Check Snap to basemap layers.
- Click OK.