Area is the second method and often represents the physical size of the data item. It can for example be a country, municipality or areas of a store. The same is true here as with the point that an area can be calculated and not physically limited by borders. This is true in the case of area of influence when you look at what people are visiting a certain store.
Normally you would want to add additional data to a map to represent a value, but I see benefits of just adding a map without anything extra just for navigational purposes. I don’t know how often you’ve encountered the same problem as me but I don’t often see people following standards when it comes to naming areas. For example when I use an app I don’t know if I should search for “United states, U.S., US” or something similar. But give me a map and I can always point out where it’s located.
If you want to add more information you’ll see that we have the issue of both position and size being occupied as visual encoding methods so the most normal case is to use color. The benefit of color is that its use can easily compare color of an area to the areas around it to see trends or outliers.
One of the issues worth noting with areas is that an area may be so small that a high value is not easily seen. This can easily be solved by pairing a map with an additional visualization such as a bar chart showing actual amount.
The final method that I will discuss in this post is flow. It often represents a physical change from one point/area to another or a dependency between them. It can be airline passengers being transported, cargo from one depot to another or the movement of an army. Of course I can’t write a post on maps without having a link to a Minardillustration!
The tricky part of flow visualization is that you often need to structure your data so that you have a departure location, destination location and a flow that connects them. But once you have it you get a powerful visualization for showing dependencies or change.
If I want to tell a user how much is being moved by the flow I can use either color or size. For example using the Minard illustration again we can see that the size of the line correlates to the soldiers in his army.
You have probably noticed the one common thread across all these mapping examples is color. It’s an important method to visually encode data and it may be something that I will write an additional post about in the future. We have yet to explore many topics regarding color so I hope you will come back to read it!