A variety of measures of national income and output are used in economics to estimate total economic activity in a country or region, including gross domestic product (GDP), gross national product (GNP), and net national income (NNI). All are concerned with counting the total amount of goods and services produced within some "boundary". The boundary may be defined climatologically, or by citizenship; and limits on the type of activity also form part of the conceptual boundary; for instance, these measures are for the most part limited to counting goods and services that are exchanged for money: production not for sale but ...