Where is Ace of Diamond set?
Japanese manga series
Ace of Diamond (2006): 1 real place Japanese Wikipedia files it under as its setting, in Japan. Wikidata records no setting for this manga at all, so this is a category rather than a statement, and it is labelled that way below. Where the manga takes place, not where it was made: a manga is drawn and filmed nowhere, so this is the only kind of location it has.
Places per Japanese Wikipedia: “甲子園球場を舞台としたアニメ作品” category
Japanese Wikipedia’s “甲子園球場を舞台としたアニメ作品” category lists 1 place. A category is an editor’s choice, not a sourced sentence, so these places are listed apart. Each links to its category.
Drawn from these real places
Japanese Wikipedia says this manga’s setting was modelled on these real places. Nothing was filmed at them.