A system enables an arbitrary number of items to be indexed in a geographic region that provides a predictable query response time across a sharded database. Items indexed to the geographic region are stored on a single shard and additional items are added to that shard as long as an overflow condition indicative of undesirable query response times is not met. If the overflow condition is met the system expands the storage of items indexed to the geographic region to one or more additional shards in order to maintain predictable query response times. The system may maintain a shard count representing the total number of shards being used to store items corresponding to a geographic region, which can be used to query one or more relevant shards. The system may apply deterministic hashing in order to evenly distribute shards across database nodes of the sharded database.