How can I set my spatial reference to the base map in arcgis api. I want to change the default spatial reference.
The spatial reference for a map is defined either by the extent passed to the map constructor or by the first layer added to the map. Checkout the any projection sample to see how to specify different spatial references for a map.
If you're using the basemap or center and zoom options with the map constructor, the map's spatial reference will be web mercator.