[realfun]

Thanks for the suggestion and there are definitely room for optimization.

In the original design we did consider approach similar to the "heatmap approach" you mentioned, it would reduce the shard movement for people who commutes in the city.

Later we figured that simply sharding along on the Hilbert Curve already give what we need, and the shard move is unavoidable, we would explain more details around the shard move in future blog.