The world economy, or global economy, is the economy of the world, considered as an international exchange of goods and services. Global economy is the economy of global society while country economies are focused within the specified country. Combining the country economies the world economy is made. Beyond the minimum standard concerning value in production, use, and exchange the definitions, representations, models, and valuations of the world economy vary widely. It is inseparable from the geography and ecology of Earth. It is common to limit questions of the world economy exclusively to human economic activity, and the world economy is typically judged in monetary terms, even in cases in which there is no efficient market to help valuate certain goods or services, or in cases in which a lack of independent research or government cooperation makes establishing figures difficult. Typical examples are illegal drugs and other black market goods, which by any standard are a part of the world economy, but for which there is by definition no legal market of any kind. However, even in cases in which there is a clear and efficient market to establish a monetary value, economists do not typically use the current or official exchange rate to translate the monetary units of this market into a single unit for the world economy, since exchange rates typically do not closely reflect worldwide value, for example in cases where the volume or price of transactions is closely regulated by the government. Rather, market valuations in a local currency are typically translated to a single monetary unit using the idea of purchasing power. This is the method used below, which is used for estimating worldwide economic activity in terms of real US dollars or euros. However, the world economy can be evaluated and expressed in many more ways. It is unclear, for example, how many of the world’s 7.13 billion people have most of their economic activity reflected in these valuations. In 2013, the largest economies in the world with more than $2 trillion, €1.25 trillion by nominal GDP were the United States, China, Japan, Germany, France, the United Kingdom, Brazil, Russia, Italy and India.