This article was written with the main purpose of showing you how to determine zones on a shard when using compound shard keys. Defining Zones in Shards means pre-defining where certain chunks will be stored and amongst which set of particular shards they will be balanced according to the shard key definition. MongoDB 4.4 brings [&]

https://www.percona.com/blog/sharding-with-zones-based-on-compound-shard-keys-on-mongodb-4-4/