Translation:This square is in the center of the city.
"Center of the city" sounds like a geographic measuring exercise to me. However, I think the most common meaning of "центр города" is simply "downtown" or "city center" - the conceptual heart as opposed to the geographic midpoint.
I suppose it is true that in most instances when one would utter this specific sentence, saying "This square is downtown" wouldn't really impart any information that wasn't already obvious just by turning one's head but "the center of the city" (as in precise geographical center) wouldn't be immediately obvious.
Could находится be omitted here? Could you say "Эта площадь в центре города. " and have the same meaning?
Looks like "plaza" is out of favour with whomever put this set together. Two in a row I tried plaza and was gonged. Added to that, it seems they don't like "town" over city and have an insatiable need to add stuff like "the" city where just where just plain old "town" would have sufficed. Bottom line, what's wrong with "this plaza is in the centre of town"?