CPTED is based on the idea that how people act and feel in a space is directly related to how it is physically designed. It is a big foundation in designing safe public spaces. There's heaps of interesting and important research about CPTED being done by designers and criminologists.
In the design of public spaces it's related to things like
- Sight lines
- Transparent materials
- Safety created by having other people around (passive surveillance)
Walk around your neighbourhood and you'll be seeing and feeling where CPTED principles are at work or not at work. You don't need to be an urban designer to know which spaces feel comfortable to you and the 'dodgy' areas you don't want to walk through. CPTED is really all about minimising and not creating those 'dodgy' spaces.