Python scatter plot. Size and style of the marker

Question

I have a set of data that I want to show as a scatter plot. I want each point to be plotted as a square of size dx.

          x = [0.5,0.1,0.3]           y = [0.2,0.7,0.8]           z = [10.,15.,12.]           dx = [0.05,0.2,0.1]            scatter(x,y,c=z,s=dx,marker='s') 

The problem is that the size s that the scatter function read is in points^2. What I'd like is having each point represented by a square of area dx^2, where this area is in 'real' units, the plot units. I hope you can get this point.

I also have another question. The scatter function plots the markers with a black border, how can I drop this option and have no border at all?

Answer 1

Translate from user data coordinate system to display coordinate system.

and use edgecolors='none' to plot faces with no outlines.

import numpy as np  fig = figure() ax = fig.add_subplot(111) dx_in_points = np.diff(ax.transData.transform(zip([0]*len(dx), dx)))  scatter(x,y,c=z,s=dx_in_points**2,marker='s', edgecolors='none') 

Answer 2

If you want markers that resize with the figure size, you can use patches:

from matplotlib import pyplot as plt from matplotlib.patches import Rectangle  x = [0.5, 0.1, 0.3] y = [0.2 ,0.7, 0.8] z = [10, 15, 12] dx = [0.05, 0.2, 0.1]  cmap = plt.cm.hot fig = plt.figure() ax = fig.add_subplot(111, aspect='equal')  for x, y, c, h in zip(x, y, z, dx):     ax.add_artist(Rectangle(xy=(x, y),                   color=cmap(c**2),        # I did c**2 to get nice colors from your numbers                   width=h, height=h))      # Gives a square of area h*h  plt.show() 

Note that:

1. The squares are not centered at (x,y). x,y are actually the coords of the square lower left. I let it this way to simplify my code. You should use (x + dx/2, y + dx/2).
2. The color is get from the hot colormap. I used z**2 to give colors. you should also adapt this to your needs

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Finally for your second question. You can get the border of the scatter marks out using the keyword arguments edgecolor or edgecolors. These are a matplotlib color argument or a sequence of rgba tuples, respectively. If you set the parameter to 'None', borders are not draw.