A map is a visual representation of an area—a symbolic depiction highlighting relationships between elements of that space such as objects, regions, and themes. For the key-value data structure, use dictionary tag instead.
Modern maps
- Google Maps
- List of online map services
- MapQuest
- Maps of the UK and Ireland
- Map of the United States
- NASA World Wind
Many maps are static two-dimensional, geometrically accurate (or approximately accurate) representations of three-dimensional space, while others are dynamic or interactive, even three-dimensional.
Although most commonly used to depict geography, maps may represent any space, real or imagined, without regard to context or scale; e.g. brain mapping, DNA mapping, and extraterrestrial mapping.
Many, but not all, maps are drawn to a scale, expressed as a ratio such as 1:10,000, meaning that 1 of any unit of measurement on the map corresponds exactly, or approximately, to 10,000 of that same unit on the ground.
Maps of the world or large areas are often either 'political' or 'physical'. Topographic maps show elevations and relief with contour lines or shading. Geological maps show not only the physical surface, but characteristics of the underlying rock, fault lines, and subsurface structures.
Maps that depict the surface of the Earth also use a projection, a way of translating the three-dimensional real surface of the geoid to a two-dimensional picture. Perhaps the best-known world-map projection is the Mercator projection, originally designed as a form of nautical chart.
Aeroplane pilots use aeronautical charts based on a Lambert conformal conic projection, in which a cone is laid over the section of the earth to be mapped.
From the last quarter of the 20th century, the indispensable tool of the cartographer has been the computer. Much of cartography, especially at the data-gathering survey level, has been subsumed by Geographic Information Systems (GIS).
A complex problem when dealing with maps is to calculate the distance between two points. The simplest approach is to work as if the map was a simple plane and use Euclidean distance function. However, this might be inadequate, especially in the case when we are dealing with large distances. In that case the differences between the real shape of the planet and a plane will get more accent. A significant improvement over this is to calculate the distance between two coordinates using the Haversine formula, but even this might be imprecise in some cases where high precision is needed, due to the differences of altitude or other geometrical, or non-geometrical distance modificators, like speed limits on roads, closed borders of countries, travel costs, etc.
