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A proportional symbol map or proportional point symbol map is a type of thematic map that uses map symbols that vary in size to represent a quantitative variable. [1]: 131 For example, circles may be used to show the location of cities within the map, with the size of each circle sized proportionally to the population of the city. Typically ...
[10] [12] Included were early chorochromatic and flow maps, and possibly the first proportional point symbol and dasymetric maps. John Snow's cholera map about the cholera deaths in London in the 1840s, published 1854. Another example of early thematic mapping comes from London physician John Snow. Though disease had been mapped thematically ...
A bivariate map or multivariate map is a type of thematic map that displays two or more variables on a single map by combining different sets of symbols. [1] Each of the variables is represented using a standard thematic map technique, such as choropleth , cartogram , or proportional symbols .
A map symbol or cartographic symbol is a graphical device used to visually represent a real-world feature on a map, working in the same fashion as other forms of symbols. Map symbols may include point markers, lines, regions, continuous fields, or text; these can be designed visually in their shape, size, color, pattern, and other graphic ...
A cartogram (also called a value-area map or an anamorphic map, the latter common among German-speakers) is a thematic map of a set of features (countries, provinces, etc.), in which their geographic size is altered to be directly proportional to a selected variable, such as travel time, population, or gross national income. Geographic space ...
A Cartogram purposefully distorts the size of areal features proportional to a chosen variable, such as total population, and thus may be thought of as a hybrid between choropleth and proportional symbol maps. Several automated and manual techniques have been developed to construct cartograms, each having advantages and disadvantages.
A typical choropleth legend for a classed choropleth map includes a series of sample patches of the symbol for each class, with a text description of the corresponding range of values. On an unclassed choropleth map, it is common for the legend to show a smooth color gradient between the minimum and maximum values, with two or more points along ...
1838 map of pre-railroad cargo traffic in Ireland, one of the first thematic maps to use proportional symbols. The earliest known map to visually represent the volume of flow were two maps by engineer Henry Drury Harness, published in 1838 as part of a report on the potential for railroad construction in Ireland, showing the quantity of cargo traffic by road and canal.