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Heat (or color coded Map) in Matlab

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CMatlabWold
CMatlabWold on 23 Jun 2020
Commented: CMatlabWold on 26 Jun 2020
Hello,
I am creating a heatmap in Matlab. For each Sewershed, there is a median income. It is in the shapefile. When I produce the Sewershape in Matlab, I get this...
The command bar reads:
17×1 struct array with fields:
Geometry
BoundingBox
X
Y
Pervious
Impervious
Sewershed
Population
Housing
Acres
Squarefeet
GallonsH2O
SymbolID
Median
This is my code:
S = shaperead('Sewershed.shp')
mapshow(S)
for i=1:17
meanValue = mean(S(i).BoundingBox);
text(meanValue(1),meanValue(2),num2str(S(i).Sewershed))
end
So, I need the median income for each sewershed to have a color scale, where the largest income is darker red and the smaller incomes become lighter... (red or any color... but darker for higher income and lighter for lower income).
Please, let me know if you can help.
Thanks
C

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Accepted Answer

Kelly Kearney
Kelly Kearney on 24 Jun 2020
In my opinion, the easiest way to do this is to alter the colors of the patches after plotting with mapshow/geoshow. An example:
S = shaperead('usastatelo');
h = mapshow(S);
set(h.Children, {'CData'}, {S.PopDens2000}'); % Add single cdata value to each based on property
set(h.Children, 'facecolor', 'flat'); % And link to the colormap
set(gca, 'clim', [5 500]);
An alternative would be to take a look at the makesymbolspec function, and the 'SymbolSpec' option for mapshow. But I find that option horribly unintuitive, inflexible, and a little buggy.

  3 Comments

CMatlabWold
CMatlabWold on 24 Jun 2020
Thank you! This works perfectly.
I excluded set(gca, 'clim', [5 500]);
For some reason, it wasn't working for me.
I went to edit the color map. I wanted the color to be "Summer". Is there anyway to add that to the code.
Also, is there a way to add a legend that shows the values for the colors or at least the min and max?
Thanks again!
Kelly Kearney
Kelly Kearney on 24 Jun 2020
The 'clim' bit was just an example... that line sets the color limits of the figure (the example data I showed had a few high outliers, so I wanted to narrow the color range from the defailt). You can stick with the defaults, or choose limits that are appropriate to your data.
If you want to change the colormap and add a colorbar, simply add
colormap(summer);
colorbar;

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More Answers (1)

KSSV
KSSV on 23 Jun 2020
Arrange all your mean values in an array.
M = mean(S(:).BoundingBox) ; % get all means in an array
rgb = vals2colormap(M,'jet') ; % get the respective colorcode for M
figure
hold on
for i = 1:17
patch(S(i).X,S(i).Y,rgb(i,:)) ;
end
colorbar

  2 Comments

CMatlabWold
CMatlabWold on 23 Jun 2020
Thank you.
I used the function and the code; however, the color does not show.
Of my structural array, there are 17 fields. The only field where I need a color density is the "Median".
Where would I incorporate this into the code?

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