If you’ve ever wondered how to split an area fairly without starting a territorial argument, Thiessen polygons (also called Voronoi polygons) are your new best friend. Think of them as the GIS equivalent of drawing invisible “zones of influence” around points, each polygon claiming the area closest to its point compared to any other.

Imagine dropping a bunch of coffee shops onto a map. A Thiessen polygon tells you exactly which shop is closest for any location. It’s like a “nearest caffeine provider” map, but way more versatile.

How do they help us in GIS?

Thiessen polygons are incredibly handy whenever we need to divide space based on distance. A few fun examples:

Which weather station owns this rain?

When multiple weather stations surround an area, it’s not always obvious which station should represent the rainfall there. Thiessen polygons solve this by dividing the landscape into zones based on proximity: every point inside a polygon is closest to its corresponding station.

Meteorologists use these polygons to fairly assign rainfall measurements across a region—ensuring each drop is “credited” to the nearest station. This creates cleaner spatial averages, improves hydrological models, and avoids skewing rainfall totals just because one station is closer than the others. No guesswork, no bias—just pure, geometric fairness.

Which area does each substation in the electrical grid actually serve?

By placing the locations of all substations on a map and generating Thiessen polygons, you can create an approximate service area for each one. Since every Thiessen polygon shows the region closest to a specific substation, it gives a quick, distance-based estimate of who that substation is likely powering.

While real-world grid design also depends on line capacity, terrain, and load balancing, Thiessen polygons offer a fast and intuitive way to visualize potential coverage zones, spot gaps, and plan where additional substations might relieve demand.

Where does each coastal region’s ocean territory begin?

Coastal and marine planners can extend administrative boundaries from the shore out into the ocean—right out to the Exclusive Economic Zone (EEZ). With Thiessen polygons, every point along the coast gets a fair slice of the sea pie.

In ArcGIS Pro, you can combine Thiessen polygons with tools like Intersect and Merge to extend onshore administrative boundaries offshore, all the way to a country’s EEZ. It’s a simple, elegant way to let the coastline decide which admin unit inherits which piece of the ocean—no arguing, no guesswork, just geometry doing its thing.

Below, you will find a video that exemplifies this example!

Thiessen polygons are fun to explore but even more fun to use!

Whether you’re mapping rain, fish, people, or pizza delivery zones, they’re one of the most surprisingly powerful tools hiding in your GIS toolbox. Want to give your spatial analysis superpowers? Start with a Thiessen polygon, and let the map do the talking.