Rocks and Water

Matplotlib perceptually-uniform colormaps as QGIS color ramps

Due to the substantial limitations of Python's default colormat Jet, a few Python programmers (Stéfan van der Walt, Nathaniel Smith and Eric Firing) created some perceptually-uniform colormaps for Matplotlib. The benefit of perceptually-uniform colormaps is that we perceive the color ramp to be linear (so it doesn't look like there are numerical discontinuities or breaks in slope in an actually-smooth dataset), the colormap is still very effective for the many people with colorblindness, and the ramp still works well when printed (or just viewed) in black and white. See this nice post for a good comparison and discussion of the different colormaps.

I use QGIS quite a bit as my default GIS system (Arc is expensive and has less interoperability with FOSS geospatial data types). The benefits of perceptually-uniform color ramps certainly extend to geospatial data and analysis, so I've ported the color ramps to the QGIS color ramp XML file (here).

Here are some images (from the blog post linked above) displaying the new colormaps:

Magma Magma

Inferno Inferno

Plasma Plasma

And my favorite,

Viridis Viridis

Here's a map of coseismic slip model of the 2015 Gorkha, Nepal earthquake from Galetzka et al 2015:

Gorkha slip

And you can do geospatial analysis in your Lisa Frank fantasy Earth by using the Inferno color ramp for topography (with topo stresses on the Tibrikot-Dogari fault shown as well):

Thakkhola graben

To install the color ramps, save the file and in the QGIS menu, go to Settings -> Style Manager -> Color ramp and hit the green Plus sign and select the file.

<!DOCTYPE qgis_style>
<qgis_style version="0">
  <symbols/>
  <colorramps>
    <colorramp type="gradient" name="Magma">
      <prop k="color1" v="0,0,3,255"/>
      <prop k="color2" v="251,252,191,255"/>
      <prop k="stops" v="0.04;4,4,21,255:0.08;14,10,42,255:0.12;26,16,65,255:0.16;40,17,89,255:0.20;57,15,110,255:0.23;74,16,121,255:0.27;90,21,126,255:0.31;105,28,128,255:0.35;121,34,129,255:0.39;137,40,129,255:0.43;153,45,127,255:0.47;169,50,124,255:0.51;185,55,120,255:0.55;202,62,114,255:0.59;217,70,106,255:0.62;230,81,98,255:0.66;240,96,93,255:0.70;247,113,91,255:0.74;251,132,96,255:0.78;253,151,104,255:0.82;254,170,116,255:0.86;254,188,130,255:0.90;253,207,146,255:0.94;253,225,163,255:0.98;252,243,181,255"/>
    </colorramp>
    <colorramp type="gradient" name="Inferno">
      <prop k="color1" v="0,0,3,255"/>
      <prop k="color2" v="252,254,164,255"/>
      <prop k="stops" v="0.04;37,5,145,255:0.08;56,4,153,255:0.12;73,2,159,255:0.16;89,1,164,255:0.20;104,0,167,255:0.23;120,1,168,255:0.27;134,7,166,255:0.31;149,17,161,255:0.35;162,28,154,255:0.39;174,39,145,255:0.43;185,51,136,255:0.47;195,62,127,255:0.51;205,73,117,255:0.55;214,85,109,255:0.59;222,96,100,255:0.62;229,108,91,255:0.66;236,120,83,255:0.70;242,133,74,255:0.74;247,146,65,255:0.78;250,160,57,255:0.82;253,175,49,255:0.86;253,190,41,255:0.90;252,206,37,255:0.94;248,223,36,255:0.98;242,240,38,255"/>
    </colorramp>
    <colorramp type="gradient" name="Plasma">
      <prop k="color1" v="12,7,134,255"/>
      <prop k="color2" v="239,248,33,255"/>
      <prop k="stops" v="0.04;37,5,145,255:0.08;56,4,153,255:0.12;73,2,159,255:0.16;89,1,164,255:0.20;104,0,167,255:0.23;120,1,168,255:0.27;134,7,166,255:0.31;149,17,161,255:0.35;162,28,154,255:0.39;174,39,145,255:0.43;185,51,136,255:0.47;195,62,127,255:0.51;205,73,117,255:0.55;214,85,109,255:0.59;222,96,100,255:0.62;229,108,91,255:0.66;236,120,83,255:0.70;242,133,74,255:0.74;247,146,65,255:0.78;250,160,57,255:0.82;253,175,49,255:0.86;253,190,41,255:0.90;252,206,37,255:0.94;248,223,36,255:0.98;242,240,38,255"/>
    </colorramp>
    <colorramp type="gradient" name="Viridis">
      <prop k="color1" v="68,1,84,255"/>
      <prop k="color2" v="253,231,36,255"/>
      <prop k="stops" v="0.04;71,15,98,255:0.08;72,29,111,255:0.12;71,42,121,255:0.16;69,54,129,255:0.20;65,66,134,255:0.23;60,77,138,255:0.27;55,88,140,255:0.31;50,98,141,255:0.35;46,108,142,255:0.39;42,118,142,255:0.43;38,127,142,255:0.47;35,137,141,255:0.51;31,146,140,255:0.55;30,155,137,255:0.59;32,165,133,255:0.62;40,174,127,255:0.66;53,183,120,255:0.70;69,191,111,255:0.74;89,199,100,255:0.78;112,206,86,255:0.82;136,213,71,255:0.86;162,218,55,255:0.90;189,222,38,255:0.94;215,226,25,255:0.98;241,229,28,255"/>
    </colorramp>
  </colorramps>
</qgis_style>

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