1. A system for servicing photon map queries, comprising: a memory resource storing data locating photon points dispersed in a multi-dimensional scene and an acceleration structure including nodes that respectively define surfaces that each spatially bound a selection of the photon points, the selections of varying relative granularity, and the nodes arranged in a graph with edges connecting pairs of nodes; an interface for accepting a plurality of queries from one or more code modules, the queries each defining a respective spatially-located volume; and an acceleration structure traversal resource configured for traversing the acceleration structure with the queries, wherein the traversal is performed with collections of the queries, each collection associated with a node of the acceleration structure and comprising queries for which the traversal resource has detected overlap between the spatially-located volumes of those queries and the surface defined by that acceleration structure node, the further traversal of queries deferrable by the traversal resource on a collection-by-collection basis, and while deferring collection, the traversal resource is capable of adding further queries to each collection.