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Five Years of Drought

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Why we love it

This award-winning set of maps sets a new standard in analysis and visual storytelling. The bivariate hexbin mapping technique proves to be as gorgeous and sophisticated as it is intuitive. We love how these maps capture the geographic and historic complexity of this epic US drought. Combining five years of weekly data, the maps uncover how conditions vary in both intensity and length. Color indicates severity while size indicates frequency. For example, large deep purple symbols indicate where exceptional drought was experienced almost continuously for five years. This is geographic analysis at its best.

Why it works

The main map stands on its own while supplemental maps give a different perspective on the same data. This works because it adds nuance to the story and shows the care taken by the mapmaker. It also highlights that there is no single “best” way to tell a story. The judicious use of call-outs directly on the maps, the powerful legend, and the minimal-yet-elegant basemaps combine to turn a big, messy dataset into understanding. Wise use of an equal-area projection ensures each hexbin indicates the same sized area. A companion blog post explains how anyone can re-use this work.

Important steps

  • Prepare data for use

    Download, merge, and weight the raw weekly data into a single five-year aggregate.
    How to make this map

  • Experiment with hexbin grid sizing

    Experiment to get an appropriately sized hexbin grid small enough to see important variation, but still legible when zoomed out.
    Why use hexagons?

  • Use spatial join to put data into hexbin cells

    Pour the data into the hexbin cells by aggregate intersecting polygons via spatial join.
    Learn about spatial join

  • Create a bi-variate map

    Use Smart Mapping styling to create a bi-variate map with layer splitting and symbology.
    Learn more about splitting
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Requirements

  • Data

    Shapefiles that delineate the contours of drought severity are produced and archived each week by the United States Drought Monitor. US state outlines and terrain came from ArcGIS Living Atlas of the World. Software used: ArcGIS Pro, Story Map Cascade Template.
    View the United States Drought Monitor
    View ArcGIS Living Atlas of the World

  • Analysis

    Use the Merge tool to merge individual weeks of data into a single shapefile. Use the generate tessellation tool to convert multiple overlapping drought severity polygons into a hexagon tessellation scheme weighted by source data (by both severity and frequency).
    Generate tessellation tool

  • Time

    Some unknown amount of time was spent in downtime-daydreaming and playing around with color palettes and cell sizes. Actual production time of the physical map was around five hours, including some exploratory dead ends. It took a further day to craft the story map and blog.
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Tips and tricks

  • Create seamless switches when user zooms

    The interactive version of the map seamlessly switches to graduated numbers once the user has zoomed in far enough to show local details.

  • Show intense drought areas by grouping circles

    Size the graduated circles so the largest just start to coalesce into a single blob of drought.

  • Use hillshading to give basic orientation

    The elegant and restrained basemap with hillshading provides enough information to orient the reader but keeps the focus on the thematic cartography.
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Resources

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Headshot of John Nelson, map author

Map Author

John Nelson

I have way too much fun looking for ways to understand and present data visually, engage users, and write about it. Otherwise, I’m chasing around toddlers and wrangling chickens. Life is good.

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If you liked this map, check out these other Maps We Love that explore similar topics.

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