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Working with multiple data frames

Adding insets or small multiples can be as much about clarity as it is about leading your map reader through the map in a specific way. In Chapter 2, Getting Started in ArcGIS Pro, we have added a Locator Map to remind our map reader of the general location of our map data. For some maps, this is not necessary if the audience is likely to know where it is already (for example, a local map for a city council meeting), or it is such a clearly recognizable place (for example, the African continent). It's important to assess your target audience and decide if a locator adds value.

An inset map adds more detail about a specific area of the map. Insets are common on road maps, where the network of streets becomes too dense for clarity in urban centers, or to draw attention to a specific set of features on the map, as seen in the following figure. In this case, the inset is also floated over parts of the map to demonstrate its relative importance:

Figure 3.15: An inset map adds clarity and focus to specific areas of the map

Either of these can be created from new maps, or by adding a Map Frame into your layout a second time, and changing the extent, if all relevant data layers are present.

You can also insert data frames to create small multiples. A small multiple is a technique popularized by Edward Tufte for visualizing the change. As the name implies, they are multiple copies of the same map at the same small scale with little detail, to highlight changes in the data. They are a great technique for displaying the same variable at different time periods, or different variables over the same geographic extent. By repeating the same base layer at the same scale, the reader is focused on the change between maps rather than the marginalia.

Small multiples are rendered at the same scale, and organized in a line or grid to allow quick comparison. To see them in action, let's set up a new project and use our US Counties data:

Open a new project and select Blank Project
Insert a New Map
Right-click and remove the Topographic layer that automatically appears

When you add a new map to a project, ArcPro tries to save you time by including an Esri basemap. You can change this setting in Project| Options. Under Map and Scene, choose a Default basemap of your organization, or select None to create your own beautiful maps from scratch.

Add the US Counties layer from your GettingStarted folder
Click on the symbol for UScounties to open the Symbology pane
Change the method from Single Symbol to Graduated Colors
Set the Field to VACANT and Normalization to HSE_UNITS, to display the percentage of housing units that are vacant
Leave the method on Natural Breaks and set the Classes to 5
Click the drop-down for Color scheme, and check the box next to Show names
Select reds (5 classes)
Click the More button over the classifications, and select Symbols|Format all symbols
Set the Outline color to Soapstone Dust and the Width to 0.4 pt

Click Apply and the back arrow (at the top of the pane) to return to the classification scheme
Click anywhere to deselect the classes, then click the lightest symbol
Change the Outline color to Sahara Sand and click Apply (this helps reduce the amount of detail when the map size is reduced)

When displaying maps at a very small scale, often the symbol outlines can overwhelm the symbol color. Turning off outlines often results in an undesirable loss of detail. For best effect, set the Outline color slightly darker than the symbol color, and the outline as thin as possible.

Add three more map frames, and choose some variables from the table. Since this is just for practice, they don't need to necessarily make sense together. Don't forget to normalize where appropriate:

Insert a New Layout. Select ANSI Letter, Landscape orientation.
Add in print margin guides.
Insert each of your Map Frame—use the selection next to the Default to have them insert at a less than full page.
Select each Map Frame in turn, and on the Format tab, set the Width to 5 inches and height to 3.25 inches.
Align the bottom two frames with the margin guides in the corners.
Align the top two frames with the side margin guides.
Select each frame in turn, and set the Scale (in the lower-left corner of the layout window) to 1:40,000,000. You may need to type it in for the first one, and then it will be available in the list for the rest of them.
Select all four map frames (hold the Shift key and click each one) and on the Format tab, change the Current Selection to Border, and set the Line to No Color.
To complete your small multiples, you may need to add in legends, but keep them small and unobtrusive, the maps should tell the story.
Add a title that encapsulates the series, feel free to have a little fun since we're just playing with the data.

Remember, once you have a Map Frame or map element positioned and formatted just the way you want, you can lock it to keep from accidentally moving or changing it. Just click the padlock next to the item in the Contents pane.

Here's a completely random data series presented as small multiples:

Figure 3.16: Small multiples sample