Dot Maps use dots (or points) to demonstrate the existence of a subject or a feature. It’s a lot like Bubble Maps (Proportional Symbol Maps), but the dots’ sizes don’t depend on their values, as there’s no size setting. These maps are very useful and popular in the census, tourism, health service, and any other researches.
Note that when you use this type to draw density maps they must be drawn on an equal-area map projection. This is critical – using a map projection that does not preserve the size of areas will distort the perceived density of the dots.
There are two general types of Marker Maps: One-To-One and One-To-Many. One-To-One is a type where a marker stands for an only feature, event, or any other subject. One-To-Many means that one marker describes several subjects or values. There is no difference in setting the data, this is just general information that doesn’t affect the way of managing the data.
Source(s):
Rashid's Blog: An Educational Portal 