This grid has been imagined by the F.I.A.V. to codify the use of an emblem, since the same flag can have several uses. For example, it's the case of France where the civil flag and the State flag are identical.
So, the upper line is affected to flags while the lower line is affected to ensigns. Likewise, the first vertical line is affected to civil use, the second one to public or State use, and the third one to military use. The six zones so delimited are filled with a black point according to the different uses of the emblem shown.
SIMPLIFIED GLOSSARY :
Emblem : a generic word to refer to flags, ensigns, standards, and more generally any symbolic object which represents a collectivity : a State, a nation, people, etc…
Ensign : At the origin of flags, this word more specifically refers to the emblems waving on ships.
Flag : It is the name given to a piece of cloth attached to a flagstaff which was in the past used as a military sign and which in the XIXth century turned into the emblem of a nation whose colors it bears. (Larousse).
Standard : emblem reserved for a person, a king, a president, a minister, etc…
National flag : the flag which symbolizes the nation. It can cover all the uses (civil, State and military). It is often mistaken with the civil flag, usable by citizens.
Civil flag : flag used by citizens. On the F.I.A.V. grid, it is shown in zone 1.
State flag : flag used by the State or the government. On the F.I.A.V. grid, it is shown in zone 2.
War flag : flag used in wartime. On the F.I.A.V. grid, it is shown in zone 3.
Civil ensign : It is the ensign which is used by the merchant navy, sport sailing, etc…It is also named merchant flag. On the F.I.A.V. grid, it is shown in zone 4.
State ensign : Ensign used by State ships. On the F.I.A.V. grid, it is shown in zone 5.
War ensign : Ensign floating on war ships. On the F.I.A.V. grid, it is shown in zone 6.
Ratio : It is the ratio of the height or width to the length of the flag. It is generally indicated in the shape 2:3 for example for France.
Hoist : half–flag near the staff
Fly : half-flag opposite the staff
Canton : Upper quarter of the flag located near the staff, or upper half of the hoist.