SPD = Supplementary Planning Document (SPD)
Basically a set of site-specific policies that the City Council creates
(involving consultation) and which then forms the basis of additional rules
for a specific site that developers have to adhere to.
For instance, the SPD might specify "This site will be car-free with XYZ
constraints"; a future developer who comes up with a plan for the site then
has to adhere to that. They have to make sure the detail they come up with
is line with this policy.