One of the new features introduced with ArcGIS Explorer 480 is the ability to set any color in a raster image transparent. This is very handy when working with georeferenced images with "no data" values. Have a look at the video, then follow along in this post.

Let's take a closer look. First, we've added a local raster file, in this case a TIF image that was used during the California fire response last year. To add a local raster go to File, then Open, and choose Rasters, and then browse for the file you want.

In this particular file you will see that we have black areas representing "no data" surrounding the image, and blocking the view of the underlying basemap information.

To set the black areas in the image transparent, first open the raster layer properties. To do this, right click the layer in Contents, then choose Layer Properties.

In the layer properties, choose Raster Background. You can specify the transparent color in one of two ways, by typing in the actual RGB values, or by clicking on the image on the map. It's easiest just to click on the color you want transparent in the raster.

After we apply the changes, you'll see that we've turned the black RGB values transparent, and created a much nicer overlay.

For more information, see the Raster Background Color Help topic.