Strategic Housing Market Area Assessment is n essential evidence document defined in the NPPF.  Its apparent purpose is to enforce the implementation of “an objective assessment of the market-led housing need and demand” where a local authority is undertaking a Local Plan process.  The research activity is carried out by retained consultants and central government guidance requires them to speak to all commercial parties that work in the property market and the local authorities.  Part of the evidence is the local authority housing lists. There is also an assessment of ‘affordability’ and general level of house prices in relation to the other participating local authority areas and London. The boundary of the “market area” is open to interpretation and there are a number of documents available that variously define the housing market for Guildford borough, with it stretching from Rushmoor in the west to Reigate & Banstead in the north east and including Woking borough in the north down to Chichester, Hampshire in the south.  However, past SHMAA studies have defined the market area as the boroughs of Woking, Guildford and Waverley and named it the South West Surrey SHMAA.  A boundary based on local authority areas is permitted under the NPPF and recognised as a practical solution to the problem.  However, the NPPF also recognises that such a market area contains population, economic, commuting and employment dynamics and so introduces a “Duty to Co-operate” to force local authorities to have an on-going dialogue and formal process that defines potential areas in each other’s boundaries that might cater for overspill housing development between them.