ArcGIS 10.1 provides options for you to choose whether to snap to features in basemap layers and feature service layers when working in ArcMap. Previously, snapping was always enabled for all available layers, which caused performance to decrease in some cases. To enable snapping, click the Snapping menu on the Snapping toolbar, click Options, and check Snap to feature service layers or Snap to basemap layers. These options are off by default.
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.
Although you cannot edit the layers inside a basemap, you can snap to feature layers in a basemap layer. For example, if you were creating a new waterline in relation to building locations, you can still snap to the Building Footprints layer even though it is inside the basemap. Keep in mind that if your features are very large or complex, enabling snapping to basemap layers may reduce the performance benefits provided by basemap layers.
On another occasion, you are making updates to a city’s parks and recreation geodatabase. Roads and utility infrastructure data are shared with you as web-based feature services. When you are creating a new open space area in your parks geodatabase, you can snap to the roads and other features from the feature services.