London mayoral election: The lie of the land
It's a four letter word at the heart of the London mayoral election campaign.
How much is there to build on, and what should be built on it?
It's been apparent from the start of the 2016 campaign that all the leading mayoral candidates appreciate that - for the first time in five contests for City Hall - housing could be a major determinant of how people end up voting.
So - what are the early signals?
The housing issue is dense, and the policy questions complex. It's hard to see many voters getting beyond the bold-type pledges made with nice round numbers.
But genuine credibility established over the next few weeks - based around detailed solutions - could achieve cut-through.
Mainly so far the turf for this particular war has been publicly owned "brownfield" land.
It's difficult to say yet how much there might be to play with. But it was reported this week that the London Land Commission set up last year has so far identified enough for 130,000 homes.
There's a fairly big caveat attached. Much of this land is owned by agencies like the NHS, the Ministry of Defence or local government. And they have to weigh up the pressure for immediate disposal against predicting future operational needs.
Mayor's direct say
Cross-department land assembly won't be easy. But the mayor does have a direct say over land owned by Transport for London.
It claims it has now identified about 300 acres, across 75 sites, which could deliver 10,000 homes over the next decade. Two thirds of them would be in Zones 1 and 2.
There are already plans for developments at Parsons Green, Northwood and above the proposed new Tube link at Battersea power station, where affordable housing is badly needed.
Most sites are what TfL describes as "operationally constrained", adjoining or above stations or track, making development more tricky.
It means the new mayor could have, optimistically as things stand, around 1,000 new homes a year to shape directly.
We've learned so far that Labour candidate Sadiq Khan will apportion an unstipulated amount of this new housing to shared ownership where you typically start by buying 25% of a property's value and pay rent on the remaining 75%.
He says he will give priority to people who've been renting privately for more than five years, and claims he will be able to cut the typical rent element because TfL will retain the freehold.
Conservative Zac Goldsmith has said that he would ensure the land is used for a mixture of affordable rented, shared ownership and market housing which would go to people who had lived in the capital for three years.
The Liberal Democrats' Caroline Pidgeon has called for a new mayoral building company, the Greens' Sian Berry for a "community" homes agency, and UKIP's Peter Whittle for a social housing building programme alongside a debate on the pressure of migration on the current housing stock.
And what of previous experience? Over the last few years, the Greater London Authority (GLA) under Boris Johnson has sold off - rather than retaining a stake in - around 1,500 acres of land.
According to the latest GLA figures 27,300 homes have received planning consent, of which 7,590 were deemed affordable, either to rent or buy.
Mr Khan has described this as a "fire-sale" and said public assets need to be "sweated more".
In recent years, too, more than a hundred Metropolitan Police buildings have been sold, raising around £1bn.
Mr Goldsmith says that the limited physical and monetary resources available in the future means regeneration needs to combines transport and housing, and new ways of raising money for infrastructure like the mayor taking a slice of stamp duty will be necessary.