1. A selective laser solidification apparatus, comprising:a build platform for supporting a powder bed onto which powder layers can be deposited;
at least one laser module for generating a plurality of laser beams for solidifying powder material deposited onto the powder bed;
a laser scanner for individually steering each laser beam to solidify separate areas in each powder layer, a scanning zone for each laser beam being defined by the locations on the powder bed to which the laser beam can be steered by the laser scanner, and the laser scanner being arranged such that each scanning zone is less than the total area of the powder bed and at least two of the scanning zones overlap; and
a processing unit arranged to select, for at least one of the powder layers, which one of the laser beams to use to solidify an area of the powder layer located within a region in which the scanning zones overlap based on a total length of time each laser beam is used for solidifying areas in the powder layer.