# how to plot contour lines on Joint Histogram plot

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UTKARSH VERMA on 25 Feb 2021
Commented: Cris LaPierre on 7 Mar 2021
Hi all,
I am plotting joint histogram by using histogram2 as shown in figure.
I need contour lines to differentiate each color which gives clear picture of data distribution means lines to separate each color .
Can anyone help me with this?
my code for this plot as follows:
clf
figure(1)
Yedges = [0.25:.25:100];
Xedges = [50:2.5:350];
h= histogram2(olr,rf,Xedges,Yedges,'DisplayStyle','tile','FaceColor','flat')%,'Normalization','pdf')
colorbar;
colormap(hsv(15))
ylim([0 100])
ax=gca;
ax.CLim=[0 100]
And, The kind of figure I want should look like(plotted in Rstudio):
Thanks,
Utkarsh
##### 2 CommentsShowHide 1 older comment
UTKARSH VERMA on 6 Mar 2021
Hi Cris,
Here is the data which I used to plot above histogram plot.
Note:- On the x axis "noaa_olr_dly_1985_2014_AI_grid_masked_JJAS.nc" data is plotted and on the y axis "rf_daily_1985_2014_grid_JJAS.nc" is plotted.

Cris LaPierre on 6 Mar 2021
Edited: Cris LaPierre on 6 Mar 2021
I'll share a couple thoughts about how I would try to approach this.
In order to create a contour plot, MATLAB requires the inputs to be matrices. Each row corresponds to a value on the Y axis, and each column corresponds to a value on the X axis. This means the data needs to be arranged in an evenly spaced grid.
For your data, that means dividing the XY plane into bins, and counting the number of points in each bin. You can do this using histcounts2. This returns a mxn matrix where the rows corespond to your X bins, and the columns correspond to your Y bins.
Next, create X and Y matrices, also mxn, using meshgrid.
Here's a rough example using random numbers.
% Create random data
x = (randn(20000,1)*40)+200;
y = abs(randn(20000,1))*20;
plot(x,y,'.')
% Create buns and obtain counts
Xedges=linspace(0,400,51);
Yedges=linspace(0,80,21);
N = histcounts2(x,y,Xedges,Yedges);
% use bin edges to find the center of each bin in X and Y
[X,Y] = meshgrid(mean([Xedges(1:end-1);Xedges(2:end)],1),...
mean([Yedges(1:end-1);Yedges(2:end,1)],1));
% Create countor, transponsing N so rows correspond to Y and columns correspond to X
figure
contourf(X,Y,N',5,"ShowText","on")
Cris LaPierre on 7 Mar 2021

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