The main purpose of a classification of activities is to classify economic entities and statistical units, such as establishments or enterprises, according to the economic activity in which they mainly engage. The main aim is to provide a set of activity categories that can be utilised when dissecting statistics according to such activities. Different classifications are needed to cater for the different functions which statistics are required to perform, so at international and national levels classifications have been developed for a wide range of purposes, whereby each has its own specific area of application depending on the subject of classification. Economic classifications can be broadly divided into two categories: Classifications of economic activities, which aim to cover all economic activities – from agriculture to services – are used to classify economic entities (enterprises, establishments, local units or other statistical units). Such classifications therefore form the basis for compiling statistics on output, the production factors entering into the production process (input: labour, raw materials and supplies, energy etc.), capital formation or financial transactions. The international classification for activity is the International Standard Industrial Classification of All Economic Activities (ISIC), maintained by the United Nations, used at world level. Classifications of products. The outputs of the economic entities are termed products and are generally divided into goods and services and grouped according to a product classification. The international classification for products is the Central Product Classification (CPC), maintained by the United Nations and used worldwide.