The GLA is calling on developers and landowners to identify sites over 0.25 hectares  that have the potential for housing development by 28 January 2013. This information, which will be for use by officers at the GLA and the boroughs only, will not be made available for public use.  In London the housing targets have traditionally been based on perceived capacity. The more ‘deliverable’ sites that can be found – the higher the targets should be.