GIS Tips & Tricks

A weblog dedictated to the lifelong pursuit of cartographic bliss in GIS.

Monday, November 14, 2005

Matching Shade Transparency to Legend

The first time I saw ArcMAP demoed at an ESRI Users Conference in Victoria was many years ago. I remember thinking how cool the polygon shade transparency was and how I thought it would radically change the way I was mapping. Think of it: transparently shaded themed polygons over orthophotography or satellite imagery…How cool is that? Some months later when I finally got to try ArcMAP I think the first thing I did was transparently theme a land-use zones coverage over some orthophoto imagery. Wow, was I impressed! What was less impressive, unfortunately, was that ESRI seemed to go only half way with the transparency feature. Notice how your legend doesn’t change when you change the transparency of your polygons…Strange isn’t it? Maybe we are waiting for ArcGIS 10x?

Of course GIS wouldn’t be nearly as fun as it is without finding a work around solution to little software annoyances.

Here are two quick options to make your legend shade match your transparent polygons?

  1. From the TOOLS menu select the Eye Dropper tool> Customize> Commands> Page Layout> Eye Dropper
  2. Drag the Eye Dropper to an existing ArcMAP toolbar…I usually ‘drop’ it on the Drawing toolbar.
  3. With the Eye Dropper tool selected click on your transparent polygon. The RGB values of the polygon wil appear.
  4. Select OK and the transparent colour is now added to your colour palette.

Option A

  • Switch from the Eye Dropper tool to the Select Elements tool…(the arrow tool) and select the legend.
  • Right click on the legend and select CONVERT TO GRAPHICS.
  • Right click on the legend again and select UNGROUP. Do this twice to make the label patch a selectable graphic.
  • Select the patch box to change and use the Fill Colour tool…(the Paint Can) to pick the colour that was created from Eye Dropper step.

Option B

  • In the Table of Contents select the polygon layer that has had transparency applied to it. Right click the layer and select COPY.
  • Paste the copied layer back in to the Table of Contents but make sure to turn it off so the layer isn’t displayed twice in the data frame.
  • In your legend add the COPIED layer to your LEGEND ITEMS and make sure that the check box for ‘Only display layers that are checked on in your Table of Contents’ is UNSELECTED.
  • Right click the COPIED layer in the Table of Contents again and select PROPERTIES> SYMBOLOGY> match the colours in your copied layer to the colours created with the Eye Dropper tool.

Realistically the above methods are practical if you only have a handful of polygon themes with transparent shades. Also I wouldn’t suggest matching your legend to your transparent shades until you have fully committed to using those colours.

6 Comments:

  • At 6:05 PM, Anonymous Anonymous said…

    This is not a trivial thing to do accurately.

    The main reason for setting transparancy is to let another layer show through. Let's say your have an orthophoto as a background, and a 70% transparant polygon on top of it.

    Although the polygon may have a solid color as its symbology, the actual color drawn will vary depending on the pixel value of the raster below it. As the color of the ortho varies, the color of the transparancy varies as well.

    How, then, can you accurately represent it in the legend? I think most would like it shown as it would appear with a white background, but even that is not going to be accurate except in those parts of the map where the raster is white.

     
  • At 7:21 AM, Anonymous hummer010 said…

    ArcMap's handling of transparency is terrible. As soon as you have a layer with transparency set, ArcMap rasterizes all layers beneath the transparent layer. Not a real problem if the transparent layer is only above a raster already, or if you are making a raster transparent. Otherwise, all vectors under the transparent layer become a little blocky, and the file size to print becomes huge. Transparency also wrecks the export to .ai function, and can mess with the export to .pdf function.

    I try very hard to not use transparency because of these reasons. Hopefully ESRI can improve the transparency handling in future versions.

     
  • At 7:25 AM, Blogger TheGecko said…

    Great Blog with great tips. I've added you to my RSS aggregator.

    Thanks

     
  • At 6:04 PM, Anonymous Alea said…

    Sorry for bother you first.
    I have one question to ask about ArcMap, if it's convenient please answer me.
    When I export mxd file to image file, the data frame can be transparent with EMF type. But sometimes that didn't work. There must be some different setting on mxd file, but I can't find that.

    Here is a file trying to explain the question.
    The file
    Thank you so much!

     
  • At 3:32 PM, Blogger araki said…

    Hey, do you know how to make the gradient that is used in the custom box? I want to use a gradient that is like the yellow one that is standard, but can't figure out "where" to put my gradient.

     
  • At 2:04 PM, Anonymous Anonymous said…

    As a note to the Eye Dropper tool.... do not hit OK to close out of its popup unless you want to start adding new shades to your default colour palette.

     

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