How to Split a Spatial Polygon with a Line in R

Discover how to effectively `split a polygon` into two distinct areas using a line in R with the `sf` and `terra` packages. Easy-to-follow guide!
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This video is based on the question https://stackoverflow.com/q/75952151/ asked by the user 'aczich' ( https://stackoverflow.com/u/15810291/ ) and on the answer https://stackoverflow.com/a/75953843/ provided by the user 'Robert Hijmans' ( https://stackoverflow.com/u/635245/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Split a Spatial Polygon with a Line in R

When working with spatial data, one common task is to divide a polygon into two or more regions based on a specified line. This can be particularly useful when you want to analyze data points that fall within those regions or generate visual representations of them.

In this guide, we’ll take a look at how to accomplish this using R's spatial packages: sf and terra. We’ll go through step-by-step instructions on how to split a polygon using a line and visualize the outcome.

The Problem Overview

Imagine you have a simple polygon, like a square, and you want to split it into two separate regions using a vertical line. The goal is to identify how many data points fall into each of these split areas afterward and plot the polygons where the fill color represents the number of points in that region.

Required Libraries

Before we proceed, ensure that you have the necessary R packages installed:

sf: A package for handling spatial data.

terra: An updated package for managing spatial data with a focus on rasters and vector data.

You can install these packages using the following commands:

[[See Video to Reveal this Text or Code Snippet]]

Using the sf Package

Let’s start by splitting a polygon using the sf package. We'll create a polygon and a line, visualize them, and then perform the split.

Step 1: Create a Polygon and a Line

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Split the Polygon

To split the polygon, you can use the intersection function:

[[See Video to Reveal this Text or Code Snippet]]

Using the terra Package

If you prefer working with the terra package, here’s how to achieve the same split.

Step 1: Setup and Create Geometry

[[See Video to Reveal this Text or Code Snippet]]

Alternative Method with split

With terra version 1.7-23, a straightforward split function is available for this task.

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By following the steps outlined in this blog, you should be capable of splitting a spatial polygon into two distinct regions using a line in R. Whether you choose to utilize sf or terra depends on your specific needs and preferences.

Feel free to explore these methods on your data and visualize how many points fall into each of the newly created regions. Happy coding!

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