The first sentence of sharding documentation answers your question: "In sharded clusters, you can create Zones of sharded data based on the Shard key. You can Associate each zone with one or more shards in the cluster."
Before you consider sharding, have you verified that your need really needs it? As an example: today if you make a cluster on atlas it enables sharding only in M50 instances, which start at 32GB RAM and 160GB HD.
The main needs that lead you to consider sharding are database size and/or read/write volume. Considering a setup like the one I mentioned above, you already have need of sharding?
I make these considerations because sharding adds a certain complexity in database maintenance (backup, balancing of Chunks, configuration servers) that it is worth considering before if you really need.