Base Map layers provide a new type of layer functionality designed to enhance rendering performance while working in ArcMap. Base Map's layers draw continuously during navigation to help eliminate white space when panning and editing. The substantial performance increase is enabled by a fast drawing engine and back-end caching.
Base Maps support common layers, renderers, and data source types. More than one base map layer can be used in a map, but performance varies depending on the availability of hardware resources such as RAM.
Base Map layers are designed to contain pre-authored content, such as rasters or imagery. As a trade off for enhanced drawing and rendering performance, most geoprocessing tools cannot be used on Base Map layers. For example, Base Map layer symbology cannot be changed; however, key tools such as 'Identify' and 'Snap' function normally.
In ArcGIS Desktop 10, the Table of Contents displays warning flags where unsupported content, display, and performance issues exist. The Analyze Base Map layer tool helps identify errors and issues with Base Map (and other) layers.
Base Map layers are a Desktop enhancement and do not deliver performance enhancements on the server side. If a Base Map layer is in an MXD, use optimized map services to draw dynamic or cache content with the best Web performance.
Base Map layers can utilize Maplex labeling with no issues.
Time events in Base Map layers are not currently supported.