When I publish a feature layer to ArcGIS Online, is it automatically converted to WGS84 Web Mercator (Auxiliary Sphere)?
It projects 'on the fly'. If you are using a large dataset or many layers in a web app. I recommend projecting to Web Mercator Aux and then creating a web layer.
We have all of our data stored in WGS 1984 Web Mercator (auxiliary sphere) as that is the most compatible for large areas and displaying online.
As John responded. I would suggest switching to that projection for online work.
Yep that's right, and John has a great suggestion. Portal will keep the projection of the data published, but in ArcGIS Online it is all displayed in Web Mercator Aux.
Thanks everyone for the responses! I might have some follow up questions, but for now that helps...
Retrieving data ...