How to show cell values of raster in ArcGIS

Peeking Under the Hood: Seeing Raster Cell Values in ArcGIS

Raster datasets. They’re the workhorses of GIS, right? Think of them as grids, each cell holding a piece of the puzzle – elevation, temperature, land cover, you name it. But sometimes, you need to get down to brass tacks and actually see those individual cell values. Knowing how to do that in ArcGIS is key to really understanding your data and making smart decisions based on it. So, let’s dive in and explore some ways to reveal those hidden numbers.

Cracking Open Raster Attribute Tables

Now, if you’re dealing with discrete raster data – stuff where the cell values represent distinct categories, like different types of forest or soil – then a raster attribute table is your best friend. This table is like a decoder ring, linking each unique cell value to what it actually means, like “Oak Forest” or “Sandy Loam.” When you create one of these tables, ArcGIS automatically sets up columns like OID, VALUE, and COUNT. The VALUE column shows you each unique cell value, and the COUNT column tells you how many cells share that same value. Pretty neat, huh?

But here’s the thing: ArcGIS doesn’t automatically whip up these tables for every raster you throw at it. There are a few rules the raster needs to follow. First, it has to be discrete, not continuous. Think categories, not temperatures. Second, the pixel values need to be whole numbers, not decimals. And finally, it’s best if you don’t have a crazy number of unique values – ideally, less than 65,535.

If your raster fits the bill, you can build the table yourself. Just dig into ArcToolbox, find the “Build Raster Attribute Table” tool (it’s hiding under Data Management Tools > Raster > Raster Properties), and let it do its thing. If it’s not working, double check that your pixel type isn’t floating point! I’ve been there, scratching my head for an hour before realizing I missed that one.

The “Identify” Tool: Your Point-and-Click Value Finder

Sometimes, you just need to know the value of a specific cell. That’s where the Identify tool comes in handy. It’s super simple: just click on a cell in your raster layer, and a pop-up window will show you its value. It’s perfect for checking values at specific locations you’re interested in.

In ArcGIS Pro, the “Explore” tool does pretty much the same thing. And if you’re working with a bunch of overlapping layers, you can tell ArcGIS which layer’s information you want to see in the pop-up. Just tweak the popup options to “Visible Layers” or “Selected in Contents.”

Pixel Inspector: A Neighborhood Watch for Cell Values

Want a closer look? The Pixel Inspector tool gives you a more detailed view of what’s going on around a cell. Instead of just showing you one value, it displays an array of pixel values surrounding the cell you click on. Think of it as a little neighborhood watch for your raster data. You can even resize the window to see a bigger or smaller area.

One cool thing about the Pixel Inspector is that it can show you either the raw pixel values (the actual numbers stored in the raster) or the rendered values (the values after ArcGIS has applied any symbology or styling). This can be super helpful for understanding how your symbology is affecting the way your data looks.

“Get Cell Value”: Automating the Hunt

If you need to grab raster cell values as part of a larger process, the “Get Cell Value” tool is your friend. This tool lets you specify the exact X and Y coordinates of a pixel and then spits out the corresponding cell value. It’s perfect for automating tasks where you need to extract specific values based on location. I’ve used it in Python scripts to pull elevation values for thousands of points – a real time-saver!

Fake It ‘Til You Make It: Displaying Values Directly

Okay, ArcGIS doesn’t have a built-in button that just slaps the cell value right onto each cell, like some other GIS programs (I’m looking at you, SAGA-GIS!). But, there’s a workaround! You can convert your raster to point features. Basically, you turn each cell into a point located at the center of the cell, and then you assign the cell value as an attribute of that point. Then, you can label those points using the cell value attribute. Boom! Instant cell value display. It’s not perfect, but it gets the job done.

Raster Functions: On-the-Fly Analysis

Raster functions are like having a mini-GIS toolbox right at your fingertips. They let you process and analyze raster data on the fly. You can chain them together to create complex workflows that can be applied to all sorts of rasters. While they don’t directly show you cell values, they can be used to create new rasters that highlight specific value ranges or patterns. This is super useful for visualizing and understanding your data in new ways.

Troubleshooting Display Issues

Sometimes, what you see in ArcGIS isn’t exactly what you get in the underlying data. Display settings or data scaling can sometimes mess things up. Always double-check that your symbology and display settings are set up correctly so you’re seeing an accurate representation of your raster data. And if your raster values have a really small range, try multiplying them by a factor to make them more visible. I once spent hours trying to figure out why my elevation data looked flat, only to realize that the values were all between 0 and 1! A quick multiplication fixed everything.

Wrapping Up

ArcGIS gives you a bunch of different ways to get at those raster cell values. Whether you’re just curious about a single cell, trying to understand spatial patterns, or building complex geoprocessing models, mastering these techniques is key to unlocking the power of your raster data. So get out there, explore your data, and start making smarter decisions!