The basic principles are that there a 5 plant sizes represented in circles (to scale) 2m down to 300mm, trees are shown as a black cross but assumed to be 5m+ canopy, climbers shown in solid triangles and bulbs as shade over an area... the central point, tip or cross marks the planting spot. These shapes are laid out pleasingly in the sketch plan and same species/cultivar circles are grouped with a linking line. This is still a theoretical plan as no plants are actually assigned yet, it is still in the space design level of the process.
Actual plant combos can the be 'copied' from successful designers and books such as the RHS Planting Combinations by Tony Lordor Piet Oudolf - Designing with plants
Remarkably simple and no doubt efficient in reality if a little uninspiring for the plant-aholics in the group.