[Qgis-user] how to do continuous color with a special value

[Christopher Barker]

Hi folks,

I have a set of data with a bunch of polygons, each of which has a value 
representing a physical quantity. I'd like to symbolize them with a 
continuous color scheme -- all is OK.

However, the data has a "nodata" value (99.9 in this case) that I would 
like to use to make those polygons transparent. Is there any way to do 
this without pre-processing the data to remove those polygons?

Also, there seem to be severe limitations on the continuous color 
symbology anyway:

1) I'd like to be able to set what the minimum and maximum values are, 
rather than it using the min and max form the data (that might even help 
to solve my problem above -- the real data is between 0 and about 10, 
but with th 99.9s in there, I don't' get a useful color ramp.

2) is there any way to apply and/or define a colormap? have a linear 
shift form one color to another is very limiting. I don't know what GIS 
systems usually provide, but scientific plotting packages usually 
provide a bunch of stock colormaps (green to red, greyscale, etc, etc.), 
suitable for different types of data.

thanks,

-Chris





-- 
Christopher Barker, Ph.D.
Oceanographer

Emergency Response Division
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