We have an extensive collection of GIS data sitting in ArcSDE, exposed via map and feature services, and already in a regional (projected) coordinate system. We are starting to explore building web applications using HTML 5 and JavaScript, including ArcGIS API for Javascript 4.8.

If we use an ESRI basemap (e,g, streets, satellite, hybrid, topo, gray, dark-gray, oceans, osm, national-geographic), found in the Map object > basemap property, what is the process for incorporating our feature services in SRID 'xyz' with a basemap in SRID 'abc'? What if we include multiple feature services from various federal, state and local agencies with, potentially, different SRIDs?