Median age This entry is the age that divides a population into two numerically equal groups; that is, half the people are younger than this age and half are older. It is a single index that summarizes the age distribution of a population. Currently, the median age ranges from a low of about 15 in Uganda and Gaza Strip to 40 or more in several European countries and Japan. See the entry for "Age structure" for the importance of a young versus an older age structure and, by implication, a low versus a higher median age.
Merchant marine Merchant marine may be defined as all ships engaged in the carriage of goods; or all commercial vessels (as opposed to all nonmilitary ships), which excludes tugs, fishing vessels, offshore oil rigs, etc. This entry contains information in four fields - total, ships by type, foreign-owned, and registered in other countries. Total includes the number of ships (1,000 GRT or over), total DWT for those ships, and total GRT for those ships. DWT or dead weight tonnage is the total weight of cargo, plus bunkers, stores, etc., that a ship can carry when immersed to the appropriate load line. GRT or gross register tonnage is a figure obtained by measuring the entire sheltered volume of a ship available for cargo and passengers and converting it to tons on the basis of 100 cubic feet per ton; there is no stable relationship between GRT and DWT. Ships by type includes a listing of barge carriers, bulk cargo ships, cargo ships, chemical tankers, combination bulk carriers, combination ore/oil carriers, container ships, liquefied gas tankers, livestock carriers, multifunctional large-load carriers, petroleum tankers, passenger ships, passenger/cargo ships, railcar carriers, refrigerated cargo ships, roll-on/roll-off cargo ships, short-sea passenger ships, specialized tankers, and vehicle carriers. Foreign-owned are ships that fly the flag of one country but belong to owners in another. Registered in other countries are ships that belong to owners in one country but fly the flag of another.
Military This category includes the entries dealing with a country's military structure, manpower, and expenditures.
Military - note This entry includes miscellaneous military information of significance not included elsewhere.
Military branches This entry lists the names of the ground, naval, air, marine, and other defense or security forces.
Military expenditures - dollar figure This entry gives current military expenditures in US dollars; the figure is calculated by multiplying the estimated defense spending in percentage terms by the gross domestic product (GDP) calculated on an exchange rate basis, not purchasing power parity (PPP) terms. Dollar figures for military expenditures should be treated with caution because of different price patterns and accounting methods among nations, as well as wide variations in the strength of their currencies.
Military expenditures - percent of GDP This entry gives current military expenditures as an estimated percent of gross domestic product (GDP). These figures are calculated on an exchange rate basis, i.e., not in purchasing power parity (PPP) terms.
Military service age and obligation This entry gives the minimum age at which an individual may volunteer for military service or be subject to conscription.
Money figures All money figures are expressed in contemporaneous US dollars unless otherwise indicated.
National holiday This entry gives the primary national day of celebration - usually independence day.
Nationality This entry provides the identifying terms for citizens - noun and adjective.
Natural gas - consumption This entry is the total natural gas consumed in cubic meters (cu m). The discrepancy between the amount of natural gas produced and/or imported and the amount consumed and/or exported is due to the omission of stock changes and other complicating factors.
Natural gas - exports
This entry is the total natural gas exported in cubic meters (cu m).
Natural gas - imports
This entry is the total natural gas imported in cubic meters (cu m).
Natural gas - production This entry is the total natural gas produced in cubic meters (cu m). The discrepancy between the amount of natural gas produced and/or imported and the amount consumed and/or exported is due to the omission of stock changes and other complicating factors.
Natural gas - proved reserves This entry is the stock of proved reserves of natural gas in cubic meters (cu m). Proved reserves are those quantities of natural gas, which, by analysis of geological and engineering data, can be estimated with a high degree of confidence to be commercially recoverable from a given date forward, from known reservoirs and under current economic conditions.
Natural hazards
This entry lists potential natural disasters.
Natural resources This entry lists a country's mineral, petroleum, hydropower, and other resources of commercial importance.
Net migration rate This entry includes the figure for the difference between the number of persons entering and leaving a country during the year per 1,000 persons (based on midyear population). An excess of persons entering the country is referred to as net immigration (e.g., 3.56 migrants/1,000 population); an excess of persons leaving the country as net emigration (e.g., −9.26 migrants/1,000 population). The net migration rate indicates the contribution of migration to the overall level of population change.