A map is a tool for displaying dispersion and spatial differences of geographical phenomena. Normally, they use color and symbols in maps to show spatial contrasts. The size of each symbol used in a map indicates the importance of the value of the variable it represents. Using cartograms is another mode of display. In a cartogram, some thematic mapping variable is substituted for land area or distance. Cartograms are not real maps; the geometry or space of the map is distorted in order to convey the information of this alternate variable. The variables with higher value and greater size are shown with larger area and the variables with less value and smaller size are shown with less area.

Cartogram of population (2006)

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Cartogram of migrant population (2006)

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The areas of the districts 21 and 22, being larger in size than other districts but having less population, are scaled in proportion to their population. Since a change in the value of each district would result in a change in the areas of that district, as the value of the district changes in terms of population and immigration, a different cartogram is generated. Thus the districts 6, 9 and 15 provide very different areas.



Figure 2.5 Population age pyramid

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حق انتشار اطلاعات براى شهردارى تهران محفوظ است 1393 - 1385
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