Relationship maps are an easy way to visualize and compare multiple attributes from your data within ArcGIS Online.
These maps allow you to explore the relationship between two topics within a single map and help you see if they are possibly related. This new mapping option is easy to try, and can provide valuable insight about your data that you may not have found otherwise.
A relationship map combines two data patterns to see if they converge geographically. For example, here is a choropleth map showing the percentage of diabetes in the US by county.
Here, we have another thematic choropleth map showing the percent of the population classified as obese:
At a glance, these patterns look similar, but I want to see where the patterns are both high, both low, or occurring strongly on their own. Relationship mapping allows me to combine these two map patterns in order to explore where patterns overlap or diverge. So if we combine these two color ramps to show a combination of the patterns, we would get a grid and map like this:
From this map, we see that the corners tell us a great deal of information. The purple values show where high rates of both obesity and diabetes. The darkest pink values show where there is a high amount of diabetic population, but fewer people with obesity. The darkest blue values show where people are most likely to be obese, but less likely to have diabetes.
This type of map is valuable, especially when exploring your data. It can help you quickly assess if two attributes might be related.
Classically known as a bivariate choropleth map, these maps have always been possible within ArcGIS, but with a great deal of customization and forethought. Now, you can create these maps in minutes, and can easily make adjustments while you explore the data. Using Cindy Brewer-inspired color ramps, these bivariate choropleth maps show how two data patterns overlap (or don't overlap). To learn more about this mapping style and to see examples, visit this blog.
It's as easy as selecting the two attributes you want to compare!
In Map Viewer within ArcGIS Online, bring your point, line, or polygon feature service into the map. Within the Change Style layer option, select two numeric (number) attributes from your data that you are interested in seeing on the map. Smart mapping will automatically recognize that you have selected two numbers, and within your list of mapping styles, select the “Relationship” mapping style.
If you're new to the Change Style settings in ArcGIS Online, you can also circle back to this "How to Smart Map" Story Map to learn the basics.
Let's step through the creation of a relationship map to see how it is done:
To get started, click "Change Style" within the layer options.
Begin by selecting two attributes you want to compare. These need to be attributes that are numbers (integer, float, etc).
In this example, we are going to compare adults who smoke cigarettes and adults who are excessive drinkers (as recorded by the Behavioral Risk Factor Surveillance System of the CDC).
These are tracked by the 2018 County Health Rankings, and this layer is being pulled from the ArcGIS Living Atlas of the World.
Scroll down through the options to find the "Relationship" mapping style and select it.
Immediately, we can see an interesting pattern within this data. Counties in orange strongly have smokers, while counties in blue have a high amount of adults who drink excessively.
Counties in brown have a high amount of both smokers and drinkers, while Utah stands out as a state with beige as a state with few drinkers or smokers.
Next, we will select the "Options" button.
Within Options, there are many ways to customize the symbology of the map.
Let's explore these options.
The first option you see is to change the rotation of the grid within the Legend. This changes the emphasis of the Legend by putting the focus at the top of the Legend.
The default is to show where both values are high, but you can also choose one of the options from the Focus dropdown:
High - Low
Low - High
Low
None
Another way to change the map is to adjust the grid size. By default, this is set to a 3x3 grid, because it spreads the data values over 3 categories (low, middle, high). The corners show where the patterns are the strongest, so this helps differentiate the corners as areas that we would want attention.
You can also change to a 2x2 grid to show what is above or below average. You can also change to a 4x4 grid to spread the values over more colors.
There is also an option to change the classification method. This determines the data values where the colors change.
By default, the map uses quantile so that the data is spread over enough categories to show distinct differences within the map.
Use the dropdown arrow next to the attributes to view the data histogram. Here, you can also choose a normalization attribute or manually adjust the breakpoints.
Setting manual breakpoints is a useful way to add your own subject matter expertise to the map. If you know that a value or threshold is important, set the breakpoint to that value.
To change the colors within the map, go into "Symbols"
Here, there are many Cindy Brewer inspired ramps.
Click on a ramp to see how it looks within a grid.
Here, we will select the second ramp in order to see how the map changes.
There is also the option to rotate the color ramp.
In order to help our map readers understand the map better, we can also make edits to the words that appear within the corners of the Legend.
Go into the "Legend" settings to make changes to the legend colors and labels.
In this case, some simple text changes help clarify what the colors in the corners of the grid are telling us:
Yellow - Many Drinkers, Few Smokers
Blue - Many Smokers, Few Drinkers
Black - Many Drinkers, Many Smokers
White - Few Smokers, Few Drinkers
Another way to represent your data is to add a size component to the map. This allows you to use a third attribute to add context to your map.
For example, I can show where map map's pattern overlaps with areas of high or low population.
To do this, "Add Attribute" and the mapping style will change to "Relationship and Size"
If starting a new map from scratch, choose three attributes and then select the "Relationship and Size" mapping style.
The first two attributes you select show as the relationship, while the third attribute you choose will be shown by size.
Choose "Options" to make changes to the map cartography, the same way we have done through this demo.
Within the options, you can make changes to both the colors and the sizes used in the map.
This is just an introduction to the options that can be used for relationship mapping. We always encourage you to go beyond the default settings in order to tune the map to the topic you are interested in making.
For example, below is a map that uses the relationship style to show hurricane paths from 1924 to 2014. Hurricanes are the strongest when pressure is low and wind speed is high. This is shown in this map using pink. To emphasize the strongest part of the hurricanes, I rotated the legend using the "Focus" adjustment. I also used custom labels to help explain what is being seen on the map.
There are many different ways to easily create customized maps using the "Relationship" and "Relationship and Size" mapping styles. However, you can also use these styles as a way to easily explore your data. Simply select your attributes and the mapping style, and see if you find something new about your data.
There are many other additional resources to help you get started with the relationship mapping style:
- What is a Relationship Map? (blog)
- How to Make a Relationship Map in ArcGIS Online (blog)
- Relationship map examples (links at the end of this Story Map)
Don't be afraid to try this mapping style with your point, line, and polygons datasets. Just select the two attributes you want to explore, and you're on your way.
Happy Mapping!
To view the maps within this Story Map, and additional example maps using this map style, visit the following pages:
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