continuous color ramps for raster data in ArcMap
Posted 06 April 2011 - 05:33 AM
In 10.0 a new option has been added to the raster symbology dialog:
Open the raster layer's Layer Properties sheet and go to the Symbology tab
On the left, under Show, make sure it's set to use the Stretched renderer
On the right, where it has the 3 "classes", with High and Low next to the high and low values click the Labeling button
This will open a dialog titled Advanced Labeling
Set the number of intervals (this is not the number of classes, but the number of breaks between classes; so 2 intervals means you get 3 "classes")
Then click the Generate button
You can edit the color by double-clicking the color patch, or click on the value to change the break point
Once you have it set the way you want OK out of the dialogs to apply the changes
You'll see the new breaks labeled in the TOC and in the legend on the layout
Posted 06 April 2011 - 08:40 AM
Posted 07 April 2011 - 06:32 AM
With only 8 values why not use the unique values renderer? You can select a subset of the classes in the layer symbology dialog, right-click and apply a color scheme to just the selected colors. You will want to make sure you have color ramp styles set up for the red and blue colors going in the direction you want them to go. So one would go from light to dark and the other from dark to light.
Posted 07 April 2011 - 09:21 AM
The stretched renderer creates equal intervals, and you don't have any control over the ranges, so that's probably not the way to go for this case. I think you can get close to what you need if you use the Classified renderer. It's a bit trickier though. With the Classified renderer you can set the upper limit for each class, the lower limit is defined as anything above the upper limit of the next lower class. So you would need to set the upper limit for each class such that it includes everything above the upper limit of the previous class and nothing above the upper limit for the current class. I don't have data handy to try this out myself and get the correct values, but if you can try experimenting a little I think you can get it. For the zero class, for example, I think you would want the upper limit to be zero and the class below it to have its upper limit set such that it gets everything just short of zero (something like -.0001?).
Once you have the classes set up you can work on the symbols. Set the lightest and darkest colors for both the reds and the bluses and set the color you want to show for zero. Select just those classes using Ctrl + click, then right-click on them and select Ramp Colors. That does what it says, ramps between the selected colors. If you want the colors on the two color ramps to be similar in value or whatever you'll have to sort of "eyeball", adjustingthe outer colors for each ramp proportionally dakerker or brighter or whatever you are using. You can still adjust individual colors afterwards as needed, too.
I hope that helps. After this morning I may not have much access to cartotalk until next week, but I'll be sure to check back here when I can.
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