Dot density maps use dots to represent the data value associated with a boundary or region. The total number of dots in a region represents that region's data value. If you have 10,000 senior citizens in a county, and each dot represents 100 senior citizens, there would be 100 dots in the county boundary.
Dot density is particularly useful for showing raw data where one dot represents a large number of something: population, number of fast food restaurants, number of distributors who carry a brand of soda, etc.
For example, if you have a table of age demographics broken down into postal codes, you could use the dot density option to show the concentration of small children in each postal code boundary.
There are three customizing options for dot density maps. You can specify the value of one dot. For example, you have a table of population statistics, broken down by county. There are 10,000 pre-school students in Rensselaer County, New York. If you display Rensselaer County according to the number of pre-school students using the dot density method, each dot could represent 200 students. In that case, there would be 50 dots in Rensselaer County. You can specify the number of units each dot represents using the Customize Dot Density Settings dialog box.
When you increase the value each dot represents, you decrease the number of dots that display on the map. You could modify your dot density map so that one dot represents 400 students. In that case, there would only be 25 dots in Rensselaer County.
A second option is to change the size of the dots according to your needs, either large or small. If you are working with large populations, or large counts of something, make the dot size smaller so that the distribution of dots is easier to see.
Conversely, if your working with a small data set, making the dot size larger might illustrate your analysis more clearly.
Thirdly, in the Customize Dot Density Settings dialog box, change the color of the dot to either red or black to add more variety to the final map. In this dialog box, you can select Circle or Square dot thematics and specify the dot density width (in pixels) of the square or circle. In general, squares look clearer at small sizes. At larger sizes, it may be more appropriate to use circles. You can create multiple dot density maps on the same layer by varying these options.
In the Create Thematic Map - Step 3 of 3 wizard panel, click Customize Settings. This opens the Customize Dot Density Setting dialog box. Here you can change the number of units that each dot represents, and also select the dot shape (square or circle) size, and color. You can specify a circle size from 2 to 25 pixels in width. For a square, the size can range from 1 to 25 pixels.