The decision on what to call public health is partly semantic, as the domain called 'public health' has changed over time. 'Classical' or 'traditional' public health had an external, environmental focus and produced major infrastructure projects such as sewage and safe drinking water systems, and other improvements to the human environment. Figure 3 shows changes in the conceptualisation of public health over time in two axes: populationindividual and proactive-responsive. In the figure, quadrant D describes the 'new' public health (and 'social' health, with a health equity focus) as a proactive population approach. contrasted with public health and adds to the confusion about what public health is. Figure 4 shows how such confusion can arise from the intersection of public health with other perspectives on health-such as, a population health approach, and definitions of preventive health, and primary health care.