what is dot map?
Dot maps or dot distribution map (also known as dot density map) is a map type that uses a dot symbol to show the presence of a feature or phenomenon.
Dot maps rely on a visual scatter to show spatial patterns.
in other words, A dot map is a statistical map that uses dots of fixed size to represent a fixed number of units in a particular area.
They employ a base map of a concerned area and a dot is drawn exactly on the appropriate location on the map.
they are useful in representing statistical data like population, plants in the forest, and so on
population density maps are often dotted maps
all dot maps must be drawn on an equal-area map projection. this is critical because using map projection which does not preserve the size of the area will distort the perceived density of the dots
types of dot maps
one to one dot maps where one dot represents one object or count
one to many dot maps in which one dot stands for number of things or a value (for example 1 dot represent 10000 acres of wheat production
The following are advantages of dot maps:
- If well constructed it shows the distribution and comparative densities
- It is easier to show variation in the distribution of a wide variety of commodities if it is presented using different colors.
- Dot maps are used to represent a wide range of items like population, the value of minerals, crops, and so forth
- dot maps are easy to read even to layman
- by counting the symbols it is possible to determine the original data
- They are very easy to construct compared to proportional circles
- It is very easy to compare the distribution of items considering the concentration of dots.
- the dots can be converted into choropleth or isopleth but these maps can not be transfered into dot maps
- more than one element can be shown on single map by using multiple dot map method
- this is the best method for showing the absolute figures
- dot maps work fine in black and white, when colour is not an option
- your data need not be tied to enumeration units and hence some of the concern inherent in the choropleth maps can be side stepped with dot maps.
uses of dot maps
dot maps are used to visualize distribution and densities of a big number of discrete distributed single objects by using dots which represent a constant number of objects
quantitative symbols of fixed size
the most simple dot maps uses a point symbol for a defined number of identical objects. the difficulty is to find an appropriate shape and size for the symbol as well as the value of it.
quantitative symbol of variable size
quantitative symbol of variable size can be used if the map depict an area where the object density is heterogenous and where it is difficult to find an appropriate symbol of fixed size. therefore different sizes of the symbol can be assigned to different values
example of data set appropriate for dot maps
- the distribution of car dealership in belgium (1 dot=1 dealership)
- earthquake epicentre across pacific for the last 10 years I1 dot = 1 epicentre)
- number of people by country (1 dot = 100000 people)
things to keep in mind when making dot maps
- include the legend that shows how many units of data are represented with each dot
- use the same size dots and ensure the size of each dot is appropriate for the scale and the size of the map
- ensure that colours are distinguishable
- use an albers equal area projection when making dot maps