Overlaid rasters has white edges in ArcMap

Banishing White Edges: Making Your Overlaid Rasters Play Nice in ArcMap

Ever layered rasters in ArcMap and ended up with those annoying white lines where they meet? Yeah, me too. It’s like a digital paper cut on your map! Those stark white borders can really mess with the visual appeal and, more importantly, the accuracy of your work. But don’t worry, there are ways to kick those white edges to the curb.

Why the White Lines, Though?

So, what’s the deal with these unwanted borders? Usually, it boils down to how ArcMap deals with areas where there’s no data – those spots are often tagged as “NoData,” and ArcMap can show them as white. Think of it like a blank canvas showing through. Also, if you’re using compressed image formats like JPEGs, those can sometimes introduce subtle color quirks, especially around edges and white areas, which ArcMap might misinterpret as actual white.

Time to Ditch the White: Proven Solutions

Alright, let’s get down to brass tacks. Here’s how you can wave goodbye to those pesky white edges:

1. The “Display Background Value” Trick:

This is often the first thing I try, and it’s surprisingly effective. Basically, you’re telling ArcMap, “Hey, treat white as transparent.”

• Head to the Symbology tab in your raster layer’s properties.
• Tick the “Display Background Value” box.
• Pop in “255” as the value – that’s the magic number for white in most color systems.

2. Transparency: Your Friend in Need:

Sometimes, all it takes is a little transparency to blend those edges away.

• Jump over to the Display tab in the Layer Properties.
• Start nudging the transparency slider until those white lines vanish. Easy peasy.

3. Ditch Lossy Compression (If You Can):

If you suspect those white edges are due to JPEG artifacts, consider using a lossless format like LZW when you create or export your rasters. It’s like choosing higher-quality ingredients for your map. Also, make sure your pyramids – those lower-resolution versions used for faster display – are built using lossless compression too.

4. Mosaic Datasets: The Big Guns:

If you’re wrestling with a ton of raster data, mosaic datasets are a game-changer. They let you stitch together multiple rasters into a single, virtual image, with all sorts of cool querying and processing options. And, crucially, they give you tools to get rid of those pesky borders.

5. “Build Footprints” with Radiometry: A Border Patrol for Your Data:

Within mosaic datasets, the “Build Footprints” tool (using the “Radiometry” method) is your secret weapon. It lets you tell ArcMap to ignore certain pixel values along the edges. For example, if your white borders have a pixel value of 255, you can set the maximum data value to 254, effectively telling ArcMap to ignore anything that’s pure white.

6. Resampling: Blending the Seams:

Resampling changes the pixel size of your raster, and sometimes that’s enough to smooth out those white edges. The “Resample” tool offers different techniques like Nearest Neighbor, Bilinear Interpolation, and Cubic Convolution. Which one you choose depends on your data – Nearest Neighbor is good for discrete data (like land cover classes), while Bilinear and Cubic Convolution are better for continuous data (like elevation).

7. NoData Values: Setting Boundaries:

Make sure your NoData values are properly defined. ArcMap can then display those areas as transparent, getting rid of the white fill.

8. Tweak Those Default Rendering Options:

Sometimes, ArcMap’s default settings can actually make the white edges more noticeable. You can adjust these in ArcMap Options, under the Raster tab. Try disabling custom rendering defaults or setting the stretch type to “None.”

A Few Things to Keep in Mind

• Know Your Data: The best solution really depends on what kind of raster data you’re working with.
• Compression Matters: Lossless is almost always better to avoid those pesky artifacts.
• Pyramids and Stats: Building pyramids and calculating statistics helps ArcMap display your rasters correctly and efficiently.
• ArcGIS Pro is Your Friend (Eventually): While these tips are for ArcMap, ArcGIS Pro handles transparency and raster display a bit better, so it might be worth considering down the road.

Dealing with white edges in ArcMap can be a bit of a pain, but with these tricks up your sleeve, you’ll be creating seamless, beautiful maps in no time!