LeadSled
Re. the 1200 AGL, in general terms, ICAO wise, the whole of the volume of any class of controlled airspace is available for aircraft operating in that airspace.
It is aircraft in Class G that are required to maintain a buffer (in this case below) controlled airspace
As I said, the ICAO SARP is that the whole of the volume of "controlled airspace", right to the boundary, is available to aircraft in that airspace.
Annex 11 - Chapter 2
2.6 Classification of airspaces
2.6.3 The requirements for flights within each class of airspace shall be as shown in the table in Appendix 4.
Note.— Where the ATS airspaces adjoin vertically, i.e. one above the other, flights at a common level would comply with requirements of, and be given services applicable to, the less restrictive class of airspace. In applying these criteria, Class B airspace is therefore considered less restrictive than Class A airspace; Class C airspace less restrictive than Class B airspace, etc.
In a 'lateral' boundary sense,
inside CTA/R it is generally half the applicable standard i.e. 2.5nm if the standard applicable is 5nm [surveillance based] from the lateral boundary. Australia have a filed difference allowing half of the 3nm standard [where applicable] i.e 1.5nm from the lateral boundary.
Aircraft in G [and former GAAP, soon to be ICAO D in VMC] can operate up to the boundary of the laterally adjoining CTA/R airspace.
As for the rest [SID's and Mapping] No further comment is necessary
