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In general, basemaps with tiling schemes that are different than that of the current basemap are excluded from the widget. If the default basemap is a dynamic layer, you can switch to either dynamic layers or ArcGIS tiled map service layers. If the default basemap is a tile layer, you can switch to either tile layers with the same tiling scheme or dynamic layers. For the best performance, it is recommended that all basemaps added to the gallery be cached (tiled) layers.
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See the following list of supported and unsupported basemaps in the Basemap Gallery widget:
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