Karshvar is a mythical concept in Zoroastrianism which explains the geography of the world. Basically, it describes the universe as a flat disk-shaped area divided into several concentric rings or circles. Just like you might see on a target board.
In the center of the karshvar, there is the highest peak, which is the holy mountain of Hara Berezaiti. From this mountain, rivers flow outwards, forming the seven regions of the karshvar. The first region, closest to the center, is called the Airyana Vaeja. This region is said to be where the original homeland of the Iranian people was located.
The second region is the Hapta-Həndu, or the seven rivers. This is the region where the Indus River and other surrounding rivers were located.
Beyond the Hapta-Həndu, there is the third region called the Arəzahi, which is where the famous city of Babylon was located.
The fourth region, called the Fradadhafshu, is located beyond the Arəzahi and is said to be where the kingdom of the Greeks was located.
The fifth region is the Vourū-kasha, which is where the Sassaanian empire of Persia and later Islamic Empires were located.
Beyond the Vourū-kasha is the sixth region, called the Khvaniratha. This is where the nomadic Scythians resided.
Finally, the seventh region is the Vizishtātema, also called the Werezhe, which is the farthest region from the holy mountain of Hara Berezaiti.
So, in short, karshvar is a concept that describes the geography of the world as a flat disk-shaped area divided into seven concentric circles or regions, each with its own unique characteristics and significance in Zoroastrian mythology.