They are slightly different but it is not unusual for them to be confused. I was just taking issue with Jerry's claim that the "visa" was unnecessary for the trip to Mexico. He argued that because Oswald was lazy and cheap that he would not have gone to the trouble of obtaining it or a passport and therefore this is evidence of an impersonator establishing a paper trail. Of course Oswald needed a passport to get to Cuba which was the whole point of his Mexico trip. Obtaining a passport had nothing to do with Mexico. And the "visa" which was actually a "tourist card" was necessary for him to gain entry to Mexico. Thus, both documents were necessary for him to achieve his objective and were not superfluous evidence of someone establishing a paper trail on his behalf.
We see this evidence - eyewitness accounts, physical evidence, circumstantial evidence - as proof or at least powerful evidence that he did go to Mexico City.
A conspiracist, with a conspiracy mindset, sees the exact same evidence as proof that he didn't go, that it was an impostor. Because it's all faked.
That, in brief, is the gulf between the two sides. We say up is up and down is down; they say, as Garrison said you had to see things, up is down and down is up.