Plot raster map with custom colormap

I have a matrix map_data associated with referencing object R (both in attached MAT-file). I want to map it with a discrete colorbar given an irregular range of values to look something like this:

How can I do this using geoshow or something else?

I'm using MATLAB r2014b. Here is the relevant information for the colormap:

                                  R    G    B
  0     <= map_data < 0.001     204  204  204
  0.001 <= map_data < 0.005     153  153  153
  0.005 <= map_data < 0.01      255  255  178
  0.01  <= map_data < 0.05      254  204   92
  0.05  <= map_data < 0.1       253  141   60
  0.1   <= map_data < 0.25      240   59   32
  0.25  <= map_data < 0.5       189    0   38
  0.5   <= map_data < 1           0    0    0

Thanks in advance.

Answer 1

[Sam]

Thanks to Will at Stack Overflow , who suggested using histc(). This is still not using the Mapping Toolbox though, which would be nice.

my_colormap = [204  204  204
               153  153  153
               255  255  178
               254  204   92
               253  141   60
               240   59   32
               189    0   38
                 0    0    0]/255 ;
binEdges = [0 0.001 0.005 0.01 0.05 0.1 0.25 0.5 1] ;
labels = textscan(num2str(binEdges*100),'%s') ;
labels = labels{1} ;
labels{length(labels)} = [labels{length(labels)} '%'] ;

[~,indices] = histc(map_data,binEdges);
indices(isnan(map_data)) = NaN ;
indices(isinf(map_data)) = NaN ;

figure ;
pcolor(indices-1)   % Instead of image(), to display NaN values as white
shading flat
axis equal tight

colormap(gca,my_colormap);   % gca as first argument prevents 
                             % colormap from changing for all 
                             % subsequent plots
h = colorbar;
caxis([0 length(binEdges)-1])
h.YTickLabel = labels ;

Answer 2

[Chad Greene]

I take philosophical issue with binning values from a continuous range unless those exact bins are used as discrete categories for your work. I don't know anything about the application, but as a general rule of thumb I say let continuous variables be depicted by continuous colormaps. Perhaps plot in log scale? Here's my stab at it. I couldn't load your referencing matrix R so I made up a grid that seems approximately right. Below I'm using Stephen Cobeldick's brewermap function and my rgb function to define colors.

% Load data:
load 'matlab_20160111.mat';

% Initialize map: 
worldmap('world')
geoshow('landareas.shp','facecolor',0.8*[1 1 1])

% Plot gridded data: 
[lon,lat] = meshgrid(-179:2.5:179,-89:2:89);
pcolorm(lat,lon,log10(100*map_data)); 

% Set colorbar with log10 scale: 
caxis([0 2]) 
cb = colorbar; 
set(cb,'ytick',log10([1 5 10 50 100]),...
    'yticklabel',num2str([1 5 10 50 100]'))
ylabel(cb,'percentage of some variable')

% Define colormap and background color: 
colormap(brewermap(256,'reds'))
setm(gca,'ffacecolor',rgb('ocean blue'))

[Mahmoud Solomon]

I followed this procedure and was able to generate this map. However, I have tried manipulating the code to plot only for specific region but this has not work. Can you please help me out?

[Chad Greene]

Mahmoud: Try specifying the map region when you call worldmap.

Answer 3

[Walter Roberson]

See https://www.mathworks.com/matlabcentral/answers/377542-how-can-i-change-number-on-colorbar-caxis#answer_300478 to see how to create a colormap with the desired properties without binning the data itself.

[Mahmoud Solomon]

Thanks for your response but I was talking about the plot itself and not the colorbar. I want to plot on the map but for a specific region and not the entire map.