# Generate a geographical heat map

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Maurilio Matracia on 20 Jan 2021
Edited: Adam Danz on 3 Mar 2021
Hello,
I am trying to generate a heat map on mapping toolbox.
Here I have the coordinates of the centers in my grid:
Lat = 54.2 + 0.1/6 * [11 9 7 5 3 1]' * ones(1,3) ;
Lon = 9.15 + 0.025 * ones(6,1) * [1 3 5] ;
coord = [ [Lat(:,1) , Lon(:,1)] ; [Lat(:,2) , Lon(:,2)] ; [Lat(:,3) , Lon(:,3)] ] ;
So coord is a 18 by 2 matrix, referring to the coordinates of 18 points.
Let us assume I want to assign a random value to each point, then I can define
values = rand(18, 1) .
How can I generate a heat map with such values in such locations?
How can I make each 'pixel' of the heat map like a sqare with size 0.05 by 0.033 degrees in longitude and latitude?
Thank you in advance for your help :)
##### 2 CommentsShowHide 1 older comment
Maurilio Matracia on 20 Jan 2021
The idea is to convert the numbers present in "values" into the colors of the heatmap and assign them to the respective points defined by the coordinates. So you have 2D coordinates to which you assign a 1D set of values and you get a 3D heatmap

Adam Danz on 20 Jan 2021
Edited: Adam Danz on 3 Mar 2021
I think this is what you're looking for.
heatmap
Note the change in inputs from matrix to vector of unique values.
rng('default') % for reproducibility
Lat = 54.2 + 0.1/6 * [11 9 7 5 3 1]';
Lon = 9.15 + 0.025 * [1 3 5]' ;
values = rand(18, 1);
valuesMatrix = reshape(values(:),numel(Lat),numel(Lon));
hm = heatmap(Lon,Lat,valuesMatrix);
imagesc with text labels
rng('default') % for reproducibility
Lat = 54.2 + 0.1/6 * [11 9 7 5 3 1]';
Lon = 9.15 + 0.025 * [1 3 5]' ;
values = rand(18, 1);
valuesMatrix = reshape(values(:),numel(Lat),numel(Lon));
figure()
h = imagesc(Lon, Lat, valuesMatrix);
% reproduce heatmap's colormap
n=256;
cmap = [linspace(.9,0,n)', linspace(.9447,.447,n)', linspace(.9741,.741,n)'];
colormap(cmap);
axis xy
colorbar()
hold on
% Add text labels
[xTxt, yTxt] = ndgrid(h.XData, h.YData);
labels = compose('%.4f', h.CData');
th = text(xTxt(:), yTxt(:), labels(:), ...
'VerticalAlignment', 'middle','HorizontalAlignment','Center');
geodensityplot & geoscatter for geoaxes
The types of graphics objects that can be plotted to geographic axes are limited. Some options are geobubble | geodensityplot | geoplot | geoscatter | geodensityplot; see the documentation for an updated list. The first two examples below use geodensityplot where each coordinate influences a radius of 3000 meters and the third demo uses geoscatter.
rng('default') % for reproducibility
Lat = 54.2 + 0.1/6 * [11 9 7 5 3 1]';
Lon = 9.15 + 0.025 * [1 3 5]' ;
values = rand(18, 1);
valuesMatrix = reshape(values(:),numel(Lat),numel(Lon));
[LatMatix, LonMatrix] = ndgrid(Lat,Lon);
figure()
tiledlayout(2,2)
nexttile
h = geodensityplot(LatMatix(:), LonMatrix(:), valuesMatrix(:),'Radius',3000);
nexttile
h = geodensityplot(LatMatix(:), LonMatrix(:), valuesMatrix(:),'Radius',3000,'FaceColor','interp');
nexttile
h = geoscatter(LatMatix(:), LonMatrix(:), 600, valuesMatrix(:), 'filled','Marker','s','MarkerFaceAlpha',.4);
[latlim, lonlim] = geolimits();
geolimits(latlim+(range(latlim)*.1),lonlim) % 10% lat axis increase
Adam Danz on 21 Jan 2021
This is actually the first time I'm using geodensityplot and maybe the second time I've used geoscatter. The documentation I linked to contains lots of examples to follow. geodensityplot does not currently have an option to change the shape of the markers. But geoscatter does.
I've update the answer to suggest some solutions.

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