Location:
* At (for a specific place)
* In (for a location within something)
* On (for a surface)
* To (for direction)
* Near (for proximity)
* Around (for a general area)
* There (for a specific location that has already been mentioned)
Circumstance:
* When (for time)
* How (for method)
* Why (for reason)
* What (for what is happening)
Example:
* Where is the library? (At what location is the library?)
* Where did you go? (To what place did you go?)
* Where did you find it? (In what place did you find it?)
* Where is your friend? (Near what location is your friend?)
To find the best synonym for "where," consider the context and the specific meaning you want to convey.