I'm returning to Esri products after a decade away. I first learned on ArcGIS 9 but switched to FOSS alternatives and have never touched ArcGIS Pro or ArcGIS Online (AGOL) until the last few weeks.
How do I check my map's projection in ArcGIS Online's Map Viewer (classic or new)?
If I understand correctly, the map viewer's map projection is determined by the projection of the basemap, and any layers in another system will be projected on-the-fly for a visual match. But I've seen several sources saying "don't keep layers in the web Mercator projection if you want to do spatial analysis" - because of the Mercator distortion away from the equator.
I do not know what my basemap's projection is.