Depends where you're playing. Different places have different rulesets. If you just wanna know for your own personal games then there is no answer; perhaps 'whatever feels like cheating is cheating' might be the best way to go with that. Other than that CivAssist is generally considered to be fine, though some say you shouldn't use it to get info that you wouldn't be able to get in game. In fact, that might be a better motto, 'If the tool allows you to see what you can see in game faster, use it'.