A map that focuses on a specific theme connected to a particular geographical area is called a thematic map. These maps include themes about population, languages, average rainfall, etc. These maps use shades, line patterns or dots to indicate a particular theme. If we want to know the theme of the ten largest countries in the world, we will consult a thematic map.
A thematic map is a type of map specifically designed to show a particular theme connected with a specific geographic area.
Overview
A 'Thematic map' is a map that focuses on a specific theme or subject area. This is in contrast to general reference maps, which regularly show the variety of phenomena—geological, geographical, political—together.[1][2] The contrast between them lies in the fact that thematic maps use the base data, such as coastlines, boundaries and places, only as points of reference for the phenomenon being mapped. General maps portray the base data, such as landforms, lines of transportation, settlements, and political boundaries, for their own sake.[1]
Thematic maps emphasize spatial variation of one or a small number of geographic distributions. These distributions may be physical phenomena such as climate or human characteristics such as population density and health issues. Barbara Petchenik[3] described the difference as "in place, about space." While general reference maps show where something is in space, thematic maps tell a story about that place[4] (e.g., city map).
Thematic maps are sometimes referred to as graphic essays that portray spatial variations and interrelationships of geographical distributions. Location, of course, is important to provide a reference base of where selected phenomena are occurring.
History
An important cartographic element preceding thematic mapping was the development of accurate base maps. Improvements in accuracy proceeded at a gradual pace, and even until the mid-17th century, general maps were usually of poor quality. Still, base maps around this time were good enough to display appropriate information, allowing for the first thematic maps to come into being.
One of the earliest thematic maps was a map entitled Designatio orbis christiani (1607) by Jodocus Hondius showing the dispersion of major religions, using map symbols in the French edition of his Atlas Minor (1607).[5] This was soon followed by a thematic globe (in the form of a six-gore map) showing the same subject, using Hondius' symbols, by Franciscus Haraeus, entitled: Novus typus orbis ipsus globus, ex Analemmate Ptolomaei diductus (1614)[6]
An early contributor to thematic mapping in England was the English astronomer Edmond Halley (1656–1742).[1] His first significant cartographic contribution was a star chart of the constellation of the Southern Hemisphere, made during his stay on St. Helena and published on 1686. In that same year he also published his first terrestrial map in an article about trade winds, and this map is called the first meteorological chart.[7] In 1701 he published the "New and Correct Chart Shewing the Variations of the Compass", see first image, the first chart to show lines of equal magnetic variation.
Another example of early thematic mapping comes from London physician John Snow. Though disease had been mapped thematically, Snow’s cholera map in 1854 is the best known example of using thematic maps for analysis. Essentially, his technique and methodology anticipate principles of a geographic information system (GIS). Starting with an accurate base map of a London neighborhood which included streets and water pump locations, Snow mapped out the incidents of cholera death. The emerging pattern centered around one particular pump on Broad Street. At Snow’s request, the handle of the pump was removed, and new cholera cases ceased almost at once. Further investigation of the area revealed the Broad Street pump was near a cesspit under the home of the outbreak's first cholera victim.
Another 19th-century example of thematic maps, according to Friendly (2008), was the earliest known choropleth map in 1826 created by Charles Dupin. Based on this work Louis-Léger Vauthier (1815–1901) developed the population contour map, a map that shows the population density of Paris in 1874 by contours or isolines