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Elaborate Hack for Transparency

ArcGIS supports transparency*.
* Some restrictions apply.

But if you really want to do anything with transparency you quickly learn that the functionality available is completely inadequate.

I work with a number of layers that rather than resembling a stain glass window with neatly segmented regions, come closer to resembling the outcome of tossing said window down a flight of stairs. The smashed bits all laying in a pile overlapping each other sometimes seven or eight layers deep.

But how to represent this mess? In ArcGIS you really can't because ArcGIS only draws the top most layer. Take a yellow piece of stained glass and drop it on top of a blue one and in the overlap you don't get green, but blue. Even when you set transparency!

The only way to complete our Glad bag analogy is to make two independent layers with transparency applied. Not bad when there's only two. But what if there's 582? That would take a while. And what if the layer with 582 is constantly growing so we'd have to make new definition queries or static shapefiles every single time we appended a record. Not doable.

However while ArcGIS does not support transparency properly, it occurred to me that ArcIMS does.

With that idea, I present:

Hacking ArcGIS - Lesson 1: True Transparency

Step 1: Author a new map .AXL in which includes transparency (0.6 works well) and displays by unique value.
NOTE: I don't use Author at all in more, but it works great for building a unique values display.

Step 2: In ArcIMS Administrator create a new image service using the .AXL

Step 3: Add the new image service to your ArcGIS map.

Step 4: Use a copy of the layer with display set to transparent to label.

That's it! You can now print and export a map with true transparency.


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