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I'm using QGIS to make maps of the maize, rice and wheat cultivated area at global level. I found these great netCDF files: http://www.geog.mcgill.ca/landuse/pub/Data/175crops2000/NetCDF/

Here's an example of the maps that they can generate: Maps

I have loaded the maize, rice and wheat files as layers in QGIS, and get a rainbow of colors. Problem is, I have no idea what they mean. According to the legend on the map above, the color scale indicates "% of total area"; the same datasets were used - I think - for this map, where the legend indicates "Cassava area (Percent cropland)".

Both those legends are bit cryptic (and the colors I get in QGIS are around 40). So I'm trying to locate where in QGIS I can find the "official" legend and descriptions of what the colors indicate. I followed the steps here and the legend I got was just the names of the three layers, with no colors. If I try just one layer, I get the name of the layer and nothing else.

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QGIS sees four bands inside the netcdf file, and tries to create an RGBA (red-green-blue-transparency) image out of it. This might make little sense.

You get a better result if you click on the layer, go to the style tab, and change the colouring from multicolour to one-band-pseudocolour. Then you can classify the data, and you will get a legend in the table of layers too.

You can select the band you want to be displayed, but there is not much info what the 4 bands should contain. You have to ask the authors of the data about that.

  • That worked. Using "WhiteGreen" to color the map, I can export each layer separately, each with a legend of 5 colors, ranging from 0 to a max of 0.121379 for maize, 0.203603 for wheat and 0.105435 for rice. But what is unit of measure? Is that somwehere in the files? The only thing that came with the files - this: geog.mcgill.ca/landuse/pub/Data/175crops2000/… - doesn't help. Any advise? – plugincontainer Dec 7 '14 at 17:28
  • further to... The netcdf files are linked to from this page - geog.mcgill.ca/~nramankutty/Datasets/Datasets.html "Harvested Area and Yields of 175 crops" where it mentions 4 levels. I'm interested in Level 1, harvested area, but the individual crop layers in QGIS have no sub-layers. Would the levels be my bands? – plugincontainer Dec 7 '14 at 17:41
  • Think I got it - band 3 alone looks like "Administrative level", so assuming band 1 is level 1, harvested area. – plugincontainer Dec 7 '14 at 18:19
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    You can change the colouring Mode from Continuos to Equal interval to get more than 5 colours. Naming of the levels/bands is indeed a bit confusing. – AndreJ Dec 7 '14 at 18:31

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