A map is a representation of spatial relationships among places, objects, or phenomena. Most maps depict part or all of Earth on a flat surface, using symbols to communicate location, distance, direction, and other characteristics. Unlike a photograph, a map selects and organizes information for a particular purpose. Maps may be printed or digital, and their subjects range from local streets to global distributions. The discipline concerned with their conception, production, and study is cartography. (support.esri.com)
Representation and design
Maps translate geographic information into a visual language. Points can represent settlements, lines can represent roads or a river, and areas can represent lakes or land-use zones. A legend explains the symbols, while labels identify features. Color, line weight, and symbol size distinguish categories and establish visual priorities. Titles, scale information, and coordinate grids help establish what a map shows and how it can be interpreted. (ordnancesurvey.co.uk)
Because maps are smaller than the places they represent, their contents undergo cartographic generalization. Features may be selected, simplified, combined, or displaced to remain legible. A settlement represented by individual buildings on a detailed map may become a single symbol on a regional map. These changes are deliberate adaptations to scale rather than necessarily errors in the underlying information. (ordnancesurvey.co.uk)
Scale, coordinates, and projections
Map scale expresses the relationship between distance on a map and corresponding distance on the ground. At a nominal scale of 1:25,000, one centimeter represents 250 meters. A large-scale map, such as 1:10,000, generally shows a smaller area in greater detail than a small-scale map, such as 1:1,000,000. The terminology refers to the size of the fraction, not the physical dimensions of the sheet. (ngmdb.usgs.gov)
Locations can be specified using latitude and longitude, or by coordinates in a planar grid. Ptolemy’s ancient geographic compilation used a network of latitude and longitude to locate thousands of places; modern national mapping also uses grid references to communicate positions. These systems allow locations to be identified independently of their names. (loc.gov)
A map projection transforms positions on a curved Earth into positions on a plane. This necessarily introduces distortion. Different projections preserve or approximate different properties, including area, local angles, distances, and directions. Equal-area projections preserve relative areas but distort shapes; conformal projections preserve local angles but not areas everywhere. Projection choice therefore depends on the map’s extent and intended use. (usgs.gov)
The Mercator projection is useful for navigation because constant-bearing routes appear as straight lines. It greatly enlarges areas at high latitudes, however, making it unsuitable for comparing the sizes of polar and equatorial regions. Distortion can be much smaller when an appropriate projection is applied to a limited geographic area. (store.usgs.gov)
Major types
General-reference maps show several kinds of information together, including settlements, transport routes, water bodies, and boundaries. A topographic map emphasizes the configuration of the land surface while also depicting natural and constructed features. Relief is commonly represented through contour lines, which connect points of equal elevation; closely spaced contours indicate comparatively steep slopes. (pubs.usgs.gov)
A thematic map concentrates on a subject or distribution, such as population characteristics or climate. A choropleth map shades administrative or statistical areas according to values assigned to them. Proportional-symbol maps vary symbol size to represent quantities. These methods answer different questions: a map of total population emphasizes numbers of people, whereas one of population density emphasizes concentration relative to land area. (esri.com)
Historical development
Surviving maps document varied traditions of representing space. A Babylonian clay tablet from Mesopotamia, dated approximately 700–500 BCE, depicts a schematic world with Babylon and surrounding regions. It combines recognizable geography with a culturally specific conception of the world rather than reproducing modern survey geometry. (britishmuseum.org)
In the second century CE, Ptolemy compiled geographic knowledge of the Greco-Roman world in his Geography, providing coordinates and methods for constructing maps. His work influenced European mapmaking during the Renaissance, although its geographic measurements contained substantial inaccuracies. Printing helped circulate editions containing engraved maps during the fifteenth century. (loc.gov)
Maritime mapping developed additional conventions suited to navigation. Portolan charts emphasized coastal geography and sailing routes. In 1570, Abraham Ortelius published Theatrum Orbis Terrarum, bringing maps from numerous sources into a consistently organized atlas. Its standardized presentation became influential in European atlas production. (loc.gov)
Digital mapping and interpretation
A geographic information system (GIS) stores, manages, analyzes, and displays geographically referenced data. It links locations with descriptive attributes and organizes information into layers. A map is one possible output of this system, rather than the system itself. Digital maps can combine multiple datasets and support the exploration of relationships that are difficult to identify in separate tables. (esri.com)
Digital geographic data commonly use raster and vector structures. Raster data divide space into cells containing values, while vector representations describe features through points, lines, and polygons. Their different structures suit different kinds of geographic information and analysis. (esri.com)
Interpretation depends on more than positional accuracy. Scale, projection, symbolization, classification, and the age of source data affect what a map communicates. In thematic mapping, changing class boundaries or displaying totals instead of rates can change the apparent pattern. Publication and revision dates also matter: historical map editions may differ even when they share a compilation date. (esri.com)