A server system for processing a virtual space, the virtual space comprising a plurality of entities (A-E), the server system comprising: a plurality of back-end servers ; and one or more front-end servers ; wherein each of the plurality of back-end servers is configured to store a respective subset of the plurality of entities (A-E); each front-end server is configured to be communicatively coupled to each of the plurality of back-end servers ; each front-end server is configured to be communicatively coupled to one or more client devices ; each front-end server is configured to store one or more entity references (RefA-RefE); each entity reference (RefA-RefE) comprises a first identifier for identifying a respective entity and a second identifier for identifying the back-end server on which the entity identified by the first identifier is stored; the virtual space comprises a plurality of tiles (201-206); each tile (201-206) is representative of a region in the virtual space; each entity (A-E) is located within one or more of the tiles (201-206); each of the plurality of back-end servers is configure to store a respective subset of the plurality of tiles (201-206); each of the plurality of back-end servers is configured to store only some of the entities (A-E) located in the tiles (201-206) stored by that back-end server ; and in respect of at least one of the tiles (201-206), the plurality of back-end servers are configured to store that tile (201-206), and each of said plurality of back-end servers are configured to store only a proper subset of the entities (A-E) located in that tile (201-206) such that together they store the complete set of entities (A-E) located on that tile (201-206). a plurality of back-end servers ; and one or more front-end servers ; wherein each of the plurality of back-end servers is configured to store a respective subset of the plurality of entities (A-E); each front-end server is configured to be communicatively coupled to each of the plurality of back-end servers ; each front-end server is configured to be communicatively coupled to one or more client devices ; each front-end server is configured to store one or more entity references (RefA-RefE); each entity reference (RefA-RefE) comprises a first identifier for identifying a respective entity and a second identifier for identifying the back-end server on which the entity identified by the first identifier is stored; the virtual space comprises a plurality of tiles (201-206); each tile (201-206) is representative of a region in the virtual space; each entity (A-E) is located within one or more of the tiles (201-206); each of the plurality of back-end servers is configure to store a respective subset of the plurality of tiles (201-206); each of the plurality of back-end servers is configured to store only some of the entities (A-E) located in the tiles (201-206) stored by that back-end server ; and in respect of at least one of the tiles (201-206), the plurality of back-end servers are configured to store that tile (201-206), and each of said plurality of back-end servers are configured to store only a proper subset of the entities (A-E) located in that tile (201-206) such that together they store the complete set of entities (A-E) located on that tile (201-206). <EOS>