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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 ...
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 ...
An example would be showing one variable as a choropleth map, with another variable shown as proportional symbols on top of the choropleth. A correlated symbol map represents two or more variables in the same thematic map layer, using the same visual variable , designed in such a way as to show the relative combination of the two variables.
Size, how much space a symbol occupies on a map, most commonly refers to the area of point symbols, and the thickness of line symbols, although the cartogram controls the size of area features proportional to a given variable. Size has been shown to be very effective at conveying quantitative data, and in the visual hierarchy.
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.
The variable y is directly proportional to the variable x with proportionality constant ~0.6. The variable y is inversely proportional to the variable x with proportionality constant 1. In mathematics, two sequences of numbers, often experimental data, are proportional or directly proportional if their corresponding elements have a constant ratio.
A mathematical constant is a key number whose value is fixed by an unambiguous definition, often referred to by a symbol (e.g., an alphabet letter), or by mathematicians' names to facilitate using it across multiple mathematical problems. [1] For example, the constant π may be defined as the ratio of the length of a circle's circumference to ...
A mathematical symbol is a figure or a combination of figures that is used to represent a mathematical object, an action on mathematical objects, a relation between mathematical objects, or for structuring the other symbols that occur in a formula. As formulas are entirely constituted with symbols of various types, many symbols are needed for ...