想像 and 空想: unseen situations and fantasy
Distinguish imagined content from its realism without treating imagination as verified fact.
Picturing what is not before you
想像, read そうぞう, means mentally picturing something not directly observed. 相手の気持ちを想像しました。 means imagining another person's feelings.
想像した通りでした。 says that something was as imagined. It compares imagination with what happened, but the imagined content requires context.
Freely imagined scenes
空想, read くうそう, refers to fantasy or freely imagined scenes apart from immediate reality. 空を飛ぶ町を空想しました。 means imagining a town flying through the sky.
空想の世界を描きました。 means depicting an imaginary world. Do not change this into directly observing an existing city.
Imagination and fact
想像 and 空想 can overlap. Do not impose an absolute rule making 想像 always realistic and 空想 always impossible.
それは私の想像で、確かめたことではありません。 says that something is the speaker's imagination, not something verified. Dropping the negative changes its evidential status.
Is それは私の想像で、確かめたことではありません a claim of verified fact?
Show the answer and why
No. It explicitly identifies imagination rather than something verified.