Dot maps by S. Manna, Department of Geography, Narajole Raj College

DOT MAPS

Introduction

A dot distribution map (or a dot density map or simply a dot map) is a type of that uses a point symbol to visualize the geographic distribution of a large number of related phenomena. Dot maps are a type of unit visualizations that rely on a visual scatter to show spatial patterns, especially variances in density. The dots may represent the actual locations of individual phenomena, or be randomly placed in aggregation districts to represent a number of individuals. Although these two procedures, and their underlying models, are very different, the general effect is the same.

Dot method is the most important, useful and simple method of showing distribution on the map. The simplest of all the maps that use point symbols is the one wherein the data are represented by a varying number of uniform dots, each representing the same value. This method is best suited to show the absolute figures, e.g. population, cattle, crops, minerals, industries, etc.

The idea of using dots to show relative density came about during the Industrial era of and France in the 1830s and 1840s, a time when most modern types of thematic map were developed into a relatively modern form. They were enabled by the increasing availability of statistical data and growing recognition of their value for scientific understanding. As with other types, the earliest inventions of the technique often went unnoticed, with later publications garnering much more fame. It has been claimed that the first dot distribution map was created by Valentine Seaman in a 1797 article analyzing a recent outbreak of in New York City. Although the relatively small number of case locations is not in keeping with the typical use of this technique to visualize the overall distribution of a large number of individuals, it is still noteworthy as possibly the first instance of using a map as an analytical and communication tool for social science, of , and of (even though his conclusions turned out to be incorrect). The earliest known district-based dot density map was created in 1830 by Armand Joseph Frère de Montizon (1788–????), a Franciscan friar, schoolteacher, and printer. It is a relatively simple map of population by département (administrative district) in France, with each dot representing 10,000 individuals. The map appears to have been drawn using the same technique practiced for the next two centuries and still performed by computer today: a number of dots, calculated from the total population of each department, is spread randomly across each department. The result is an intuitive visual display of population density, as higher population levels within an administrative border exhibit a closer, denser pattern of dots. Since the dots are evenly spaced, it is evident that they do not represent the actual locations of where people live within a department. This is an example of an ecological fallacy, where a value for an area generalizes all within that area to exhibit that value.

GEOGRAPHY (U.G), SEM-I I, Paper –C4T : Dot maps https://en.wikipedia.org/wiki/Dot_distribution_map, https://old.amu.ac.in/emp/studym/100010659.pdf

Dot maps by S. Manna, Department of Geography, Narajole Raj College von Mentzer's 1859 dot density map of Sweden and Norway, probably the first fully-developed representative dot density map. Although Montizon's map was the first published dot map of its type, his innovation had no effect on practice for nearly 30 years until the district-based dot density map was reinvented in 1859 in a map of the population distribution of Sweden and Norway by Thure Alexander von Mentzer, a Swedish Army officer. The dots in his map (each representing 200 residents) appear to have been based on the 1855 Census, but clearly show adjustments based on additional knowledge of population distribution. The point feature map was also reinvented in the mid-19th Century, with epidemiology again being a leading driver, especially the search for the cause of cholera, which was recognized as occurring in clear geographic patterns. Among the variety of maps created between 1820 and 1850 are some showing the locations of every case in a region. A notable example was an 1849 map by Thomas Shapter in his history of the 1832-1834 Cholera outbreak in . The map is innovative in using different point symbols to represent the cases in each of the three years. Shapter did not go so far as identifying the cause of the disease clusters he observed, his map was influential; later cited it as an inspiration for his own work.

Preparing a Dot Map

Three basic information is required to prepare a dot map. They are discussed in the following paragraphs –

1. The outline map of the concerned area with administrative boundaries.

2. Absolute figures with reference to administrative divisions

3. Relief, climate, soil, vegetation, irrigation etc., maps of the concerned area. These help use in demarcating the negative areas as well as areas of high concentration.

Following four aspects are to be properly considered for an accurate dot map.

(1) Determining the value of dot: Much of the success of the cartographer depends upon his ability to accurately fix value of the dot. If the value of the dot is too small, the dots in the areas of higher density will merge and form a dark area. On the other hand, if the value of the dot is too large, the areas of lesser density may not have even a single dot and the map may give false idea about the distribution. (2) Size of dots: The second important thing is to determine the size of dots. It should neither too small so the map looks almost empty nor it should be too large so that the map appears to be overcrowded. (3) Spacing or Placing of Dots:

GEOGRAPHY (U.G), SEM-I I, Paper –C4T : Dot maps https://en.wikipedia.org/wiki/Dot_distribution_map, https://old.amu.ac.in/emp/studym/100010659.pdf

Dot maps by S. Manna, Department of Geography, Narajole Raj College Placing of dots require great skill. Dot should not be placed over negative areas. In order to have an idea of negative areas, other maps such as relief, climate, soil, vegetation etc. should be consulted. The negative areas should be lightly marked in pencil and should be erased after the dots have been properly placed. Also dots should be concentrated in areas of high density. (4) Drawing of uniform dots: For drawing uniform dot we have to use ball - point nib and dotting nib. Sometimes, dots are punched from a black paper with the help of a punching machine and pasted on the map.

Merits of Dot Map

• Dot map is the best method of drawing distribution maps because dots show the distribution accurately. • This is the suited method for showing the absolute figure. • It gives a visual impression of distribution and also gives a bird’s eye view. • It can be converted in to data by counting the dots. • A dot map can be converted in to a shade map but a shade map can’t be converted in to dot map. • The dot map does not require any index. It is sufficient to mention the value of the dot. • A dot map can be more useful if multiple dot method is applied.

Demerits of Dot Map

• It requires sufficient practice to draw a dot map. • It is unfit to show relative data such as densities and percentages. • Sometimes enough data are not available to make an effective dot map. • For making a perfect dot map we need many other maps (e.g. relief, climate, soil, vegetation etc.). • The dot map can be faulty without the proper geographical knowledge of the concerned area. • Sometimes the scale of map is quite different from the scale of dot which gives a very misleading figure. • An inexperienced cartographer will draw a faulty map.

GEOGRAPHY (U.G), SEM-I I, Paper –C4T : Dot maps https://en.wikipedia.org/wiki/Dot_distribution_map, https://old.amu.ac.in/emp/studym/100010659.pdf

Dot maps by S. Manna, Department of Geography, Narajole Raj College

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GEOGRAPHY (U.G), SEM-I I, Paper –C4T : Dot maps https://en.wikipedia.org/wiki/Dot_distribution_map, https://old.amu.ac.in/emp/studym/100010659.pdf