Visual Analytics: Use Geo Regional Maps for Overall Comparisons
Before I started with SAS Visual Analytics, I used PROC GMAP to create choropleth maps (or geo regional maps). The maps worked for what I needed but were largely uninspired and somewhat difficult to build. I admit I never did master the skill. However, after learning to use SAS Visual Analytics geospatial objects became my favorite datavis. This is part 3 of a series about geospatial objects: Part 1 Is Location just a Distracting Character in Your Dataviz and Part 2 – Get to the point with a Geo Coordinate Map. Let’s learn how a geo regional map allows overall comparison and then how to use an info window to expand on the point.
Using a Geo Regional Map to Compare Regional Areas
Using a Geo Regional (aka choropleth) map, you can place a value over the entire region, such as a country or a state. Color is then applied over the regions to indicate a value. Choropleth is Greek for multitude of areas. In this datavis, you can see the associated property damage for the tornadoes across the areas. The darker the color the more damage the storm caused. Use an average or percentage to make the values comparable or normalized.
Look at the datavis, you can see easily see the areas of most damage but it’s harder to understand where there is the least damage. SAS Visual Analytics doesn’t offer a way to control the minimum or maximum value but you could use an overall filter.
Improving the Geo Regional Map Appearance
There are a few settings that can make your datavis a nicer for the viewer. For instance, you can add some additional data tips to provide more information when the user hovers. I use an orange for the Gradient colors because I like the color contrast against the blue ocean but I also change the Transparency to 15% so you can see the underlying state names.
In the above figure, I chose a single color for the Gradient value that is essentially light orange to dark orange. I used the darker orange on the right because I know that most people think of a larger value as darker. If I had reversed the color order it may have given the wrong signal to the user.
You can also choose to use two different colors but it makes your message a little more tricky. For instance – if you chose red to green then what are you saying? Red has a very strong association with danger. For instance a traffic light uses red to mean “STOP!” or a financial term is “being in the red” meaning there is not enough cash to pay the bills. Green however on a traffic light mean good and is generally associated with the positive. However red to green would not make sense in this instance – is there a good amount of property damage for a tornado – well probably 0. If you notice the indicator – I cannot control it and I’m using an average which doesn’t have a $0 amount. I could go monkey with the data – but it is really easy to just change the color. .
Adding an Info Window for Details
The Geo Region datavis is excellent for getting the user to focus on specific areas. It will lead to more questions so it might be convenient to use an info window to show allow the viewer to get more details about the events in that state. This info window shows the storms by duration with estimated damage. Amazing that a quick storm can result in as much damage as a long one – probably depends on where it touches down. [Check out how I created touchdown points for tornados in this post.]
The info window allows the user to click on a region and have the window pop-up to provide additional information. I used a bar-line chart but it can be anything you desire. This map is a good way to start a story – it provides an overview and helps the viewer understand where to focus their attention. In this case, Kansas and Ohio. The only downfall to the info window is that the view may not recall the values from the previous pop-up. I would use this one for more of a data discovery or as a way to entice someone into my story. Also – this data story is completely about the location and comparing how the event affected the states – it is important that geography is a character when you use maps.
Creating an Info Window
Info windows are sections that you can link to from another section. To create an info window, I first created a section and added a simple bar-line chart. Then I clicked the down arrow next to the section title and selected Display as Info Window.
Adding the Link to the Info Window
Then a link was needed from the map object to the info window. Right-click on the map, then select Add Link > Info Window Link. A pop-up window appears allowing you to select which info window you want to link to. In this case, I only have one.
When to Use a Geo Regional Maps
Use a Geo Regional map when you need to introduce a subject about location. This map helps a viewer understand where to focus their attention or understand how much variation occurs for a value. For instance, in the first figure you could see that on average Ohio had more damage per F5. My expectation was that Kansas would experience more. After hovering I learned that Kansas had almost twice as many events as Ohio.
In the last part of this blog series, we will discuss Geo Bubble maps that allow us to add show event count along with the storm damage.
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Tags: Data Visualization Tips