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How to Choose Symbology

Which symbology and analysis to use to effectively tell your story

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We all have a story to tell and maps can help visualize huge amounts of data into a gorgeous, simple image.  But how do you know which symbol to use and what do you call that dang map with bubbles? I mean circles, dots, points, or what the heck - let me just grab a piece of paper and draw it!

Well here you will learn what those lovely symbols are called and how to engage in the best dinner party conversation with something like:

"Did you see that compelling map visualization in the New York Times yesterday?"
  "Why yes, I just love the way they overlaid a dot-density over a choropleth map to show the impacts of global warming"

People will be begging for more...

Shamelessly cute sloth to keep your attention

So where to begin... how about with the person reading the map?

The average map reader will scan a map for six seconds in search of its main message. You had better be pretty deliberate in your choice of symbology to tell your story quickly and effectively.

You have only six seconds to convey your message in a map. 

In this Story Map, we will help you make a great first impression by choosing the most effective symbology. We will wrestle with:

how to use size, shape, orientation, color hue, value (lightness), texture, color saturation, transparency

how our brains perceive visual data

how data type affects color scheme

how to classify data without misleading

how to simplify crowded features with averages, prevalence, transparency and glow.

This Story Map will present a menu of symbology to choose from and offer some tips (💡) on how to use each and some sparkle (✨) to celebrate what is great about each type of symbology.

Warning: Maps Can Lie

Before whipping up a map, cartographers and communicators must first look deep down and ask some tough questions like:  

What is the story you are trying to tell?

What is the intended message? 

Who is the intended audience?

What do they think about the topic? 

What do I want them to realize?

What data do I need to tell this story?

Cartographers craft maps by selecting the information that matters most and determining how to best present it. The resulting maps selectively show what we want people to care about, so they have the power to introduce bias, distort and lie. Gasp of horror.

For more on how to lie with maps, read Mark Monmonier's How to Lie with Maps.

Know Thy Data

Data drives symbology. Make sure to pull back the curtain and look into your data. This is pretty straight-forward: 

Data can be numbers or words.

For numerical data, the number can be continuous with infinite options like weight with 1/4 pound increments or discrete with finite options like number of people.

Number of people is a discrete data type. We want whole numbers. 😱

For categorical data, the words may suggest an order (ordinal) such as small, medium, large - which has a hierarchy - or name (nominal) such as Girl Scout cookie types, eye color, or dog breed - which has no hierarchy.

Everybody knows the best is Thin Mint.

Your symbology will differ based on the type of data. For example, Numerical data are often shown as a change in symbol size or intensity of color. Nominal data are often shown as a change in symbol shape or color hue.

So let's dive in and celebrate the thematic map as the powerful rock-star communication tool it is for all things point, line, and polygon!

Symbology & Analysis for Points

Point

Graduated Symbols

Proportional Symbols

Heat Map

Clusters

Symbology & Analysis for Lines

Lines

Isolines

Direction

Flow

Symbology & Analysis for Polygons

Polygon data isn't always obvious.  Sometimes it can be symbolized using a single point or many dots.  In the end, these examples are all polygons - that is a feature with an area.

Centroid Label

Proportional Symbols

Choropleth

Predominant Category

Dot Density

Hexagons

Cartogram

Voronoi Diagram

Drive-Time

Time

Speaking of time, there are some great ways to show time and age when mapping point, line, and polygon data, but that could be a whole other story map or two or three. Check out this story map on how to show time in maps âž 

And our time is up!
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