How do we use the agr argument in st_sf()?

Decoding the Mystery of agr in st_sf()

So, you’re diving into the world of spatial data in R with the sf package, huh? Awesome! You’ve probably stumbled upon the st_sf() function, the magic wand that turns regular data into spatial data. But then you see this agr thing lurking in the arguments, and you’re like, “What’s that all about?” Don’t sweat it; let’s break it down.

Think of st_sf() as the function that glues your data to a map. The agr argument? It’s basically telling the sf package how your data relates to that map. It’s all about the connection between your attributes (those columns of data) and the shapes on your map (the geometries).

Why Should You Even Care About agr?

Well, imagine you’re working with maps and data, right? Things change. You might chop up a big area into smaller ones or combine a bunch of little areas into one big one. That’s where agr becomes your best friend. It makes sure that when you do those kinds of operations, your data doesn’t get all messed up. It ensures the values remain meaningful.

Cracking the Code: The Values agr Can Take

agr isn’t just a free-for-all; it has specific values you can use. Each value tells sf something different about how your data and map features are connected. Here’s the cheat sheet:

• “constant”: Picture this: you’ve got a field, and it’s all farmland. If you split that field, guess what? Both pieces are still farmland. That’s “constant.” The attribute stays the same, no matter what.

• “aggregate”: Now, imagine you’re looking at the population of a county. If you split that county in half, you wouldn’t expect each half to have the same population as the whole county, would you? You’d want to divide the population proportionally. That’s “aggregate.” It’s all about splitting the value based on the size of the new pieces.

• “identity”: Think about a unique identifier, like a county name. If you split “Sunnyvale County,” the resulting pieces aren’t still “Sunnyvale County,” are they? The identity is lost. That’s what “identity” signifies.

• NA_agr_: This is basically saying, “I have no idea how these things relate.” It’s the default, but honestly, it’s best to avoid it if you can.

Putting agr to Work: How to Actually Use It

Alright, enough theory. Let’s get practical. You can use agr in a couple of ways when you’re creating your spatial data frame: