Dot Maps use equally sized points placed in geographical space to indicate spatial patterns or the distribution data.

• one-to-one - one point represents the locations of individual occurrences of a phenomenon. 

• one-to-many - one dot on the map, instead of representing an individual instance, represents the presence of one or more individuals come from aggregate data. 

Dot Maps help to grasp the spatial patterns (e.g., for showing population density), but they can't be used for comparing precise values.

The dot map issues

The main concern with this type of map is that readers tend to underestimate the density of an area shown as dots. Dot technique gives the illusion of more detailed data than the solid color of a choropleth, leading to missed conclusions.