heatmap using scatter dataset python matplotlib
Question: I am writing a script to make a heatmap for scatter data on two dimensionS.
The following is a toy example of what I am trying to do:

    
    
    import numpy as np
    from matplotlib.pyplot import*
    x = [1,2,3,4,5]
    y = [1,2,3,4,5]
    heatmap, xedges, yedges = np.histogram2d(x, y, bins=50)
    extent = [xedges[0], xedges[-1], yedges[0], yedges[-1]]
    imshow(heatmap, extent = extent)
    

I should expect a the 'warmest' areas to be along y=x but instead they show up
along y=-x+5 i.e the heatmap reads one list in the reverse direction. I am not
sure why this is happening. Any suggestions?

Thanks


Answer: Try the `imshow` parameter `origin=lower`. By default it sets the (0,0)
element of the array in the upper left corner.

For example:

    
    
    import numpy as np
    import matplotlib.pyplot as plt
    x = [1,2,3,4,5,5]
    y = [1,2,3,4,5,5]
    heatmap, xedges, yedges = np.histogram2d(x, y, bins=10)
    extent = [xedges[0], xedges[-1], yedges[0], yedges[-1]]
    fig = plt.figure()
    ax1 = fig.add_subplot(211)
    ax1.imshow(heatmap, extent = extent)
    ax1.set_title("imshow Default");
    ax2 = fig.add_subplot(212)
    ax2.imshow(heatmap, extent = extent,origin='lower')
    ax2.set_title("imshow origin='lower'");
    
    fig.savefig('heatmap.png')
    

Produces:

![enter image description here](http://i.stack.imgur.com/cDl5Q.png)

