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Smart Mapping: Counts and Amounts (size)
Use different symbol sizes to represent your numerical or ranked data.
A layer of points, lines or polygons lets anyone see the location of these features relative to one another. Very often, these features on the map have numeric attributes associated with them. How can you discover and visualize meaningful patterns from these numerical attributes? How do you size these features on your map based on meaningful numbers in the real world, so that the patterns provide useful comparisons?
Libraries in Iowa, sized by population living nearby.
You can vary these features' sizes on the map when you want to compare them based on any numeric attribute, particularly for a count or total. It can also work well with an average, mean, median, rate, ratio, percent, index or other normalized data.
The Counts & Amounts (size) drawing style in ArcGIS Online and ArcGIS Enterprise applies varying sizes to your layer's features, based on a numerical attribute you choose. When the size of features varies on a map, it helps the reader immediately see where places are similar and where they are different. A logical use of size on a map does more: it also encodes how big or small those differences are, something we can see at a glance. As you will see, smart mapping helps you maximize the use of symbol size for the part of the data you want the reader to focus on.
This guide introduces easy ways to use size to discover and emphasize interesting stories in your numerical data. If your data has a numeric attribute field, it’s easy to size each feature on the map based on that field's value. Within five or six mouse clicks you will be looking at a first draft of your map.
Points example: Production Expected - Hydropower Plans and Dams in Switzerland
Lines example: Daily Traffic on Florida Roads
Polygons example: Homeless Point in Time Count, 2019, by Continuum of Care (CoC) Area
Smart mapping helps you create beautiful and informative maps, quickly. It sets the cartography of your layer based on the significant values within your data. When working in ArcGIS Online and ArcGIS Enterprise, choose Styles from the configuration toolbar to see which smart mapping styles can work with your layer.
Smart mapping helps you create beautiful and informative maps, quickly. The map's defaults jump start your exploration of the data, helping to discover meaningful values that shape the story of the data. Let's get started.
Two Steps
- Explore the numbers first. Set the breaks on meaningful values that bring out a story in the data.
- Choose sizes that emphasize the important part of the data, and de-emphasize the rest.
Smart mapping helps you follow this simple pattern. Many people set the sizes without thinking critically about adjusting the breaks which control how the sizes are applied.
You can open this web map about libraries , shown on the right, to explore on your own. The layer uses a book symbol from the POI collection (see below), but you can easily try out other symbols. Whether you choose a generic symbol, like a circle or square, or a POI symbol whose icon visually represents the item being mapped, this drawing style can size them.
ArcGIS Online and ArcGIS Enterprise users who select a layer can choose Styles from the configuration toolbar.
After you choose an attribute to map, smart mapping suggests relevant drawing styles you can try. If your attribute is an integer, smart mapping suggests the drawing style called Counts and Amounts (size) because data like total population, total sales, counts of incidents or other sums are often stored as integers.
The drawing style it suggests is only a starting point, to get you started thinking about how you might map this data. Additional drawing styles are one click away, so it is easy to try out different options quickly. Since every drawing style has its biases, strengths and weaknesses, it's important that you can explore each option easily.
1) Explore the Numbers First
Map Viewer reacts as soon as you choose attribute(s) to map, when you choose a drawing style, and when you choose a theme within that style. That instant feedback helps you see how different parts of the data can be emphasized.
Each theme helps you focus the map on meaningful parts of your data. Each theme helps tell a different story in the data.
This map at right is using the "Above" theme to emphasize values above a meaningful number. The "Above" theme sets the handles on the histogram to the mean (868.8 in this example) and the maximum value for this attribute (10,120). Why? These settings help reduce the impact of outliers or extreme values on the map's symbol sizes.
A "Size range" for the symbols is suggested, and these sizes are set to adjust automatically as the reader zooms in and out of the map.
Note how the legend is immediately useful. It shows the name of your layer, and the field alias of the attribute you chose to map. The suggested sizes are applied in proportion to the values in the attribute.
Start by looking at the histogram. Use the Zoom button just above the histogram if needed for a better look at the mean and standard deviation values above and below that mean.
The author is interested in libraries whose nearby population is larger than average, so they chose the "Above" theme and then adjusted the handles on the histogram to emphasize libraries with population between 900 and 10,000 people to make the legend more reader-friendly than the defaults (868.8 and 10,120).
The symbol is set to vary between 12 and 83 pixels wide for value between 900 and 10,000. Now that you have decided what range of population values to emphasize, you are ready to adjust their sizes.
2) Refine Sizes Last
You can create more size variation in the map by adjusting the size range. Instead of 12 and 83 pixels, try 6 and 120 to see how the larger spread between those two values stretches most of the data in the map. When you make the largest size bigger, you can also extend the upper handle on the histogram further upward toward the more extreme values, thus highlighting the biggest library in this example. Across the state, you see the mid-size libraries better than in the previous map (scroll back to the last section to compare).
By default, smart mapping scales those sizes as the user zooms in and out, which helps your map work well at multiple scales. Try different settings - every pixel makes a difference.
You may have noticed that the neutral basemap helps focus attention on the libraries. For any thematic map, you can watch your thematic map change significantly by simply switching the basemap. Click the "Basemaps" button on the left toolbar to see what basemaps are available to you. Choose the "Human Geography Map" or the "Light Gray Canvas" basemap.
Why? Each of these basemaps have what you want when making a thematic map:
- Each has almost no color in them, instead using shades of grey, black and white. When a basemap has lots of color in it, those colors compete with your thematic layer for attention.
- These basemaps put city labels and other features like water on a separate layer within the basemap, appearing on top of the thematic layer's content. This means city labels appear on top, where they can be seen. The Human Geography basemap puts water on top as well, so lakes and rivers appear on top of your thematic layer content.
You can easily try out other basemaps with one click. Hover the mouse over each to see its description.
If you don't see a neutral basemap in your list, talk to your organization's administrator to request access. They can edit the list of basemaps that appear in the basemap pane.
You can find "Human Geography" basemap and hundreds of other basemaps in Living Atlas, at the bottom of the basemaps pane.
Additional Tips
When symbols overlap, they can obscure the patterns that a map should reveal. In the example at right, the symbols around San Francisco and Los Angeles overlap and no longer look like individual features. How can you overcome this?
Try applying 50% transparency to your symbol fill when your map has many overlapping symbols. It lets the reader see the individual features again.
Add an outline color to accentuate the symbol.
On light basemaps, another option is to add a white outline and make it partially transparent. This adds a little definition at the edges of overlapping symbols, where it is needed.
When you use Counts and Amounts (size) drawing style on a polygon layer, a point symbol will be placed inside each polygon. For multi-part polygons, the point symbol will be placed in the center of the largest polygon. By default, the outline of the polygons will be a medium gray color.
A good pattern: set the outline color of the polygon to be the same color as the point symbol.
What Maps Will You Make?
You have seen how smart mapping in Map Viewer works alongside you, helping you focus on your topic and ask questions of your data. Choose an attribute, explore the drawing styles and themes within each style, adjust your breaks on the symbol sizes to use meaningful numbers, and lastly choose a symbol and set its size range to accentuate the data's story you wish to tell. Don't know which story to tell yet? Choose the "Above" theme to prompt some thinking about what you want the map to emphasize.
In just a few steps, you applied size to your layer's numerical data using the Counts & Amounts (size) drawing style. Sizing symbols for a layer of polygons, lines or points is a great option to try out when you choose to map a number.
With smart mapping doing the heavy lifting by taking the guesswork out of setting your map properties, you can freely explore new patterns and stories you did not know were present in the data.
Try it out today, and when ready share your maps with the hashtag #smartmapping and #ArcGISOnline.