The first basic military map symbols began to be used by western armies in the decades following the end of the Napoleonic Wars. During World War I, there was a degree of harmonisation between the British and French systems, including the adoption of the colour red for enemy forces and blue for allies; the British had previously used red for friendly troops because of the traditional red coats of British soldiers. However, the system now in use is broadly based on that devised by the US Army Corps of Engineers in 1917. The infantry symbol of a saltire in a rectangle was said to symbolise the crossed belts of an infantryman, while the single diagonal line for cavalry was said to represent the sabre belt. With the formation of NATO in 1949, the US Army system was standardized and adapted, with different shapes for friendly (blue rectangle), hostile (red diamond) and unknown (yellow quatrefoil) forces.

APP-6A was promulgated in December 1999. The NATO standardization agreement that covers APP-6A is STANAG 2019 (edition 4), promulgated in December 2000. APP-6A replaced APP-6 (last version, July 1986), which had been promulgated in November 1984 (edition 3 of STANAG 2019 covered APP-6), and was replaced in turn by Joint Symbology APP-6(B) (APP-6B) in 2008 (STANAG 2019 edition 5, June 2008) and NATO Joint Military Symbology APP-6(C) (APP-6C) in 2011 (STANAG 2019 edition 6, May 2011).

The U.S. is the current custodian of APP-6A, which is equivalent to MIL-STD-2525A.

The APP-6A standard provides common operational symbology along with details on their display and plotting to ensure the compatibility, and to the greatest extent possible, the interoperability of NATO land component command, control, communications, computer, and intelligence (C4I) systems, development, operations, and training. APP-6A addresses the efficient transmission of symbology information through the use of a standard methodology for symbol hierarchy, information taxonomy, and symbol identifiers.

APP-6A recognises five broad sets of symbols, each set using its own SIDC (Symbol identification coding) scheme:
• Units, equipment, and installations
• Military operations (tactical graphics)
• METOC (meteorological and oceanographic)
• Signals intelligence
• MOOTW (military operations other than war)
Units, equipment, and installations consist of icons, generally framed, associated with a single point on the map. All sorts of graphical and textual modifiers may surround them, specifying categories, quantities, dates, direction of movement, etc.

Tactical graphics represent operational information that cannot be presented via icon-based symbols alone: unit boundaries, special area designations, and other unique markings related to battlespace geometry and necessary for battlefield planning and management. There are point, line and area symbols in this category.

Meteorological and oceanographic symbology is the only set not under the standard's control: rather, they are imported from the symbology established by the World Meteorological Organization.

The signals intelligence and military operations other than war symbology sets stand apart from Units, Equipment, and Installations although they obey the same conventions (i.e., they consist of framed symbols associated to points on the map). They do not appear in APP-6A proper, having been introduced by MIL-STD-2525B.

Most of the symbols designate specific points, and consist of a frame (a geometric border), a fill, a constituent icon, and optional symbol modifiers. The latter are optional text fields or graphic indicators that provide additional information.

The frame provides a visual indication of the affiliation, battle dimension, and status of an operational object. The use of shape and colour is redundant, allowing the symbology to be used under less-than-ideal conditions such as a monochrome red display to preserve the operator's night vision. Nearly all symbols are highly stylised and can be drawn by persons almost entirely lacking in artistic skill; this allows one to draw a symbolic representation (a GRAPHREP, Graphical report) using tools as rudimentary as plain paper and pencil.

The frame serves as the base to which other symbol components and modifiers are added. In most cases a frame surrounds an icon. One major exception is equipment, which may be represented by icons alone (in which case the icons are coloured as the frame would be).

The fill is the area within a symbol. If the fill is assigned a colour, it provides an enhanced (redundant) presentation of information about the affiliation of the object. If colour is not used, the fill is transparent. A very few icons have fills of their own, which are not affected by affiliation.

The icons themselves, finally, can be understood as combinations of elementary glyphs that use simple composition rules, in a manner reminiscent of some ideographic writing systems such as Chinese. The standard, however, still attempts to provide an "exhaustive" listing of possible icons instead of laying out a dictionary of component glyphs. This causes operational problems when the need for an unforeseen symbol arises (particularly in MOOTW), a problem exacerbated by the administratively centralised maintenance of the symbology sets.

When rendering symbols with the fill on, APP-6A calls for the frame and icon to be black or white (as appropriate for the display). When rendering symbols with the fill off, APP-6A calls for a monochrome frame and icon (usually black or in accordance with the affiliation colour). NATO symbols can also be rendered with fill off using a frame coloured according to affiliation and a black icon, though this is not defined in any APP-6 standard.
• Friendly mechanized infantry with fill on
• Friendly mechanized infantry with fill off and monochrome colour frame and icon
• Friendly mechanized infantry with fill off and monochrome frame and icon
• Friendly mechanized infantry with fill off and bichrome frame and icon