This video explains how to determine the economic region of production, using isoquants and isoclines. It also analyses marginal productivity of inputs, and how this may change the production process.
The economic region of production shows the combinations of factors at a certain cost that make economic sense. Areas outside the economic region of production mean that at least one of the inputs has negative marginal productivity. This region is marked by what are called ridge lines, which are simply the boundaries beyond which one of the two factors is being overused. Therefore, outside the economic region of production, there is clear inefficiency, and the company would be better off using less of one of the two factors, bringing costs down whilst maintaining equal production output.
Learn more by reading the dictionary entry.