A Map maps something to something else.
I like to use names like uidToPerson. “To” being the shortest unambiguous way I can think of to show that I have a map.
Edit:
I’ll add that I prefer to have the map named this way, because “key” and “value” appear in that order in the name. As opposed to valueByKey. In mapping operations, the key comes first. You put(key, value) or get(key) that gives a value.
Of course this is a matter of personal preference.