Introduction to Cartography - Lecture 11

• Dot maps are constructed by letting one dot equal a certain amount of phenomenon, and then locating dots where the phenomenon is most likely to occur.
• Raw-count data are normally the basis for dot mapping.
• If possible, constrict the placement of the dots by variables (their areas/regions) that may influence the dot value.

1. generally dot maps are easy to understand
2. it is an effective way to demonstrate spatial density

1. perception of density is sometimes difficult for the map reader
2. with most digital cartographic software there is no control over the placement of dots
3. dot density per a given area is tough to map
4. it is difficult to construct any original data from the map composition because of the random placement of the dots

• centroids are commonly used when the dot represents more than one value over a given area (territorial domain)
• dot value (weight) and size can be altered to change the appearance of the dot
• dot value is the numerical value represented by each dot
• dot size is the physical space occupied by the dot
• dots should begin to coalesce in the statistical area that has the highest density
• there should be two to three dots in the area of least density
• try not to show zero dots in an area, unless you have no alternative
• select dot values that are easy to understand, i.e., 1 dot = 1,000 individuals is preferred over 1 dot = 971.5 individuals
• by altering dot size and dot value, the cartographer should be able to find an impression that is neither too busy nor too general - Experiment!



• legend design for a dot map can be difficult, many cartographers will utilize a verbal description to designate what each dot represents
• recent digital cartography programs allow the cartographer a new approach by placing representative dot densities in a legend