wide, beautiful
曼 centers on something stretched out or extended, giving the sense of wide or long. The beautiful meaning likely comes from the idea of something gracefully elongated or drawn out.
mandala
four types of mandala (in Shingon)
red spider lily (Lycoris radiata); cluster amaryllis; cluster belladonna; manjusaka
samya mandala (in Shingon); mandala where each deity is represented by an object (lotus flower, gem, sword, etc.)
Mandala of the Two Realms; Womb Realm and Matrix Realm Mandalas
Mandala of the Two Realms; Womb Realm and Matrix Realm Mandalas
four types of mandala (in Shingon)
great mandala (in Shingon); mandala with an image of each deity
Salamander (video game)
dharma mandala (in Shingon); mandala were each deity is represented by its seed syllable in Sanskrit
karma mandala (in Shingon); three-dimensional mandala with a sculpture of each deity
Garbhadhatu Mandala; Womb Realm Mandala; Matrix Realm Mandala
Garbhadhatu Mandala; Womb Realm Mandala; Matrix Realm Mandala
Vajradhatu Mandala; Diamond Realm Mandala
曼 is thought to combine 冒 (covering) and 又 (hand), suggesting a hand drawing something out or extending a cover, leading to the idea of length or width. The exact historical development is uncertain.
The top part looks like a wide eye (罒) under the sun (日), and the bottom is a hand (又). Imagine a hand stretching a wide canvas under the sun to create a beautiful, expansive scene.
For マン, picture a wide, beautiful manga (漫画) page spread out: manga -> マン, and the wide layout matches the kanji's meaning.