Welcome to the seventh class in our 2017 Economic Class series! Register for archive classes, homework and access to teachers at http://lpac.co/econ2017. Taking a long-term perspective of human development, the growth of Potential Relative Population Density isnt a smooth, continuous process, but has characteristic leaps associated with new infrastructure platforms. These infrastructure platforms define how productive the labor force can be. Currently mankind is embarking on the full development of the inland territories of the continents with high speed rail systems, and looking to the next great platform leap into nearby space.