My ArcGIS Online map has California Census Tracts. Separately, I was able to obtain an Excel spreadsheet that has Low- and Moderate-Income Census Tracts. How do I import this list and relate it to the Census Tract layer? Or must I do this in ArcGIS Desktop and connect it to my Online map?
personally I would use Add Join—Help | ArcGIS for Desktop
and a Excel To Table—Help | ArcGIS for Desktop
to get both datasets together and to ensure that the key column is of the same type. It is easier to remove any columns you don't want and just use the information you need on AGO