A basemap is a non-editable layer that provides background, or reference information, in your map or scene. A basemap provides a background of geographical context for the content you display in a map or scene. It provides a visual reference to help orient users and a framework on which you can overlay operational layers, perform analysis, and visualize geographic information. The content of a basemap is typically static and does not change frequently.
A basemap is composed of a collection of base layers (Basemap.baseLayers) and reference layers (Basemap.referenceLayers). Base layers are displayed at the bottom of a map or scene, and reference layers are displayed at the top, with the GeoModel.operationalLayers between them.
Typically, you construct a basemap using a basemap style:
Use image tile basemap styles for satellite imagery and hillshade.
Use vector tile basemap styles such as streets navigation, light gray canvas, and OpenStreetMap (OSM).
Create custom basemap styles with your own colors, glyphs, and fonts using the https://developers.arcgis.com/documentation/mapping-apis-and-services/tools/vector-tile-style-editor/.
See BasemapStyle for the full range of the basemap styles provided by Esri. Basemap styles allow you to take advantage of geographically load-balanced services and monitor usage with API keys or named users. See Basemap layers[https://developers.arcgis.com/documentation/mapping-apis-and-services/maps/basemap-layers/] for more information.
If your app works offline, you can construct a local basemap from a tiled layer using a TileCache, such as a tile package (.tpk, .tpkx, .vtpk) or a compact cache, stored on the device.
The collection of base layers in this basemap. Base layers are drawn beneath all other layers in the ArcGISMap or ArcGISScene. They are designed to provide a visual reference to help orient the user. Aerial imagery, terrain, and streets are examples of basemap layers. The collection can be empty but it is never null.