on December 25, 2022

Calculating area of pixels in continuous raster using ArcGIS Desktop?

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Decoding Raster Data: Figuring Out Pixel Areas in ArcGIS Desktop

Okay, so you’re working with GIS and have a raster image – basically a grid of cells, right? Each of those little squares holds a value, and when you’re dealing with continuous data like elevation or temperature, things get interesting. Ever wonder how much actual ground each of those pixels covers? Turns out, figuring that out is pretty important for a lot of GIS tasks. Let’s break down how to calculate pixel area in continuous rasters using ArcGIS Desktop. Trust me, it’s not as scary as it sounds!

First things first: spatial resolution. Think of it as the level of detail in your image. A pixel’s size tells you how much area it represents on the ground. Imagine a raster where each pixel is 5 meters by 5 meters. That means each pixel covers 25 square meters – a pretty good chunk of land! The smaller the pixel, the higher the resolution, and the more detail you get.

Alright, ready to crunch some numbers? Here’s the lowdown on calculating pixel area in ArcGIS Desktop:

  • Know Your Pixel Size: This is key. You gotta find out the dimensions of each pixel in your raster. Luckily, ArcGIS makes it easy. Just right-click the raster layer in your Table of Contents, hit “Properties,” and then click on the “Source” tab. You’ll see “Cell Size (X, Y)” – those are your pixel’s width and height.
  • Focus Your Efforts (Optional): Only interested in a specific area? No problem! Use the “Extract by Mask” tool to clip the raster to your area of interest. This speeds things up and keeps you focused.
  • Isolate Those Values (If Needed): Want to calculate the area for a specific range of values? The “Raster Calculator” is your friend. This tool lets you create a new raster based on a condition. Let’s say you want pixels with values between 0.1 and 0.2. The expression Con(“input_raster” >= 0.1 AND “input_raster” <= 0.2, 1) will do the trick. It creates a new raster where pixels in that range are 1, and everything else is NoData.
  • Reclassify It (Another Option): Alternatively, you can use the Reclassify tool. It’s like giving your raster a makeover, assigning new values to different ranges. Want all the values you’re interested in to be “1” and everything else to be “0”? Reclassify is the way to go.
  • Count ‘Em Up: Now, open the attribute table of your processed raster. If you don’t see one, use the “Build Raster Attribute Table” tool to create it. This table has a “COUNT” field, showing the number of pixels for each unique value. If you used the Raster Calculator to isolate a range, the “COUNT” for ‘1’ tells you how many pixels are in that range.
  • Do the Math: Time for some simple multiplication! Multiply the pixel count by the area of a single pixel. For instance, 1000 pixels with a 10m x 10m cell size equals 1000 * (10 * 10) = 100,000 square meters.
  • Get the Units Right: Finally, convert the area to whatever units you need – square kilometers, acres, hectares, you name it.

    • A Few Things to Keep in Mind:

    • Coordinate Systems Matter: Make sure your raster is in a projected coordinate system designed for area calculations. Latitude/longitude systems can mess with area, especially over large areas.
    • Cell Size Matters, Too: Pick a cell size that fits your analysis. Smaller cells mean more detail, but also more processing time. It’s a balancing act.
    • Watch Out for NoData: NoData values are usually skipped in area calculations, so be aware of them.

    Real-World Example:

    I was working on a project once where I needed to figure out the area of forested land in a region. The raster had a cell size of 30 meters. After reclassifying the raster so forest pixels were “1,” the attribute table showed a “COUNT” of 5,000 for forest.

    So, the area of forest was:

    5,000 pixels * (30 meters * 30 meters/pixel) = 4,500,000 square meters.

    That’s 450 hectares (4,500,000 square meters * (1 hectare / 10,000 square meters)). Pretty cool, huh?

    In a Nutshell:

    Calculating pixel area in rasters is a key GIS skill. By understanding how rasters work, knowing your pixel size, and using the right ArcGIS tools, you can accurately measure areas and get valuable insights from your spatial data. Just remember to double-check your coordinate system and cell size to ensure your results are spot-on! Happy mapping!

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