Each NSApp curve in Table 6 is made up of alternating constant upward gradients and vertical drops. This form is explained in Figure A-4. As the population increases, the NSApp curve passes the threshold for a G/IC facility "X" until the DSA is large enough to accommodate the population and the full site area for "X". At this point the facility can be provided and the population that can be accommodated on the remaining DSA is reduced.

For each value of DSA there is only one value for population, except where there is a vertical step in the graph. In these cases, which are not likely to occur often in practice, the population capacity varies according to whether or not it is envisaged that the relevant G/IC facility will be provided. Should this situation arise the lower population figure should be selected as it reflects adequate provision in relation to HKPSG standards, whereas the higher figure will fail to meet the HKPSG standard.

For some population values (such as P in Figure A-4) there are two associated DSAs. The lower value (A₁) will result in underprovision of G/IC facilities and the higher (A₂) in full provision. The latter is the most appropriate choice for accommodating a fixed population.