When you are indexing the 1940 census there are some location columns. If you are unable to identify the location or the spelling, I suggest that you use a google search. Do you know if the city is Las Angeles or Los Angeles? Do you know if you should be spelling the county Yavapi or Yavapai or Yavaipai? Should you be writing St Lewis or St Louis or Saint Louis?
I have the google window open while indexing. If I have a question, I put in the state; then I try to identify the county, spelling it as I believe it may be spelled. Usually I get a quick response with the spelling that I used, or a slight variation. It's quick; easy; and accurate.