Adding color to Polar Scatter plot data points

Question

I'm trying to make a polar plot with Python, of which I've been somewhat successful so far

polar scatter plot example

I did have a few questions for which I was hoping to get some ideas/suggestions:

1. is it possible set the color of the circles to a specific value (eg: "n" in the sample code below)? If so, can I set specific color ranges? Eg: 0-30: red color, 31-40: yellow; 41-60: green

Note: following the examples from Plot with conditional colors based on values in R , I tried ax.scatter(ra,dec,c = ifelse(n < 30,'red','green'), pch = 19 ) without success =(

2. how can I make the data circles a little bit bigger?

3. can I move the "90" label so that the graph title does not overlap? I tried: x.set_rlabel_position(-22.5) but I get an error ("AttributeError: 'PolarAxes' object has no attribute 'set_rlabel_position'")

4. Is it possible to only show the 0,30, and 60 elevation labels? Can these be oriented horizontally (eg: along the 0 azimuth line)?

Thank you so much! Looking forward to hearing your suggestions =)

import numpy
import matplotlib.pyplot as pyplot

dec = [10,20,30,40,50,60,70,80,90,80,70,60,50,40,30,20,10]
ra = [225,225,225,225,225,225,225,225,225,45,45,45,45,45,45,45,45]
n = [20,23,36,43,47,48,49,50,51,50,48,46,44,36,30,24,21]

ra = [x/180.0*3.141593 for x in ra]
fig = pyplot.figure()
ax = fig.add_axes([0.1,0.1,0.8,0.8],polar=True)
ax.set_ylim(0,90)
ax.set_yticks(numpy.arange(0,90,10))
ax.scatter(ra,dec,c ='r')
ax.set_title("Graph Title here", va='bottom')
pyplot.show()

Answer 1

1. colorize points
Using the c argument of scatter allows to colorize the points. In thei caase you may supply the n array to it and let the color be chosen accoring to a colormap. The colormap would consist of the different colors (31 times red, 10 times yellow, 20 times green). The advantage of using a colormap is that it allows to easily use a colorbar.

2. making circles bigger can be done using the s argument.

3. adding space between label and title This would best be done by moving the title a bit upwards, using the y argument to set_title . In order for the title not to go outside the figure, we can use the subplots_adjust method and make top a little smaller. (Note that this works only if the axes are created via subplots.)

4. Only show certain ticks can be accomplished by setting the ticks as ax.set_yticks([0,30,60]) and orienting ylabels along a horizontal line is done by ax.set_rlabel_position(0) . (Note that set_rlabel_position is available from version 1.4 on, if you have an earlier version, consider updating).

import numpy as np
import matplotlib.pyplot as plt # don't use pylab
import matplotlib.colors
import matplotlib.cm

dec = [10,20,30,40,50,60,70,80,90,80,70,60,50,40,30,20,10]
ra = [225,225,225,225,225,225,225,225,225,45,45,45,45,45,45,45,45]
n = [20,23,36,43,47,48,49,50,51,50,48,46,44,36,30,24,21]

ra = [x/180.0*np.pi for x in ra]
fig = plt.figure()
ax = fig.add_subplot(111,polar=True)
ax.set_ylim(0,90)

# 4. only show 0,30, 60 ticks
ax.set_yticks([0,30,60])
# 4. orient ylabels along horizontal line
ax.set_rlabel_position(0)

# 1. prepare cmap and norm
colors= ["red"] * 31 + ["gold"] * 10 + ["limegreen"] * 20
cmap=matplotlib.colors.ListedColormap(colors)
norm = matplotlib.colors.Normalize(vmin=0, vmax=60)   
# 2. make circles bigger, using `s` argument
# 1. set different colors according to `n`
sc = ax.scatter(ra,dec,c =n, s=49, cmap=cmap, norm=norm, zorder=2)

# 1. make colorbar
cax = fig.add_axes([0.8,0.1,0.01,0.2])
fig.colorbar(sc, cax=cax, label="n", ticks=[0,30,40,60])
# 3. move title upwards, then adjust top spacing
ax.set_title("Graph Title here", va='bottom', y=1.1)
plt.subplots_adjust(top=0.8)

plt.show()

Answer 2

for color you can use c=[list of colors for each element], for size s= like here:

ax.scatter(ra,dec,c =['r' if a < 31 else 'yellow' if a < 41 else 'green' for a in n], s =40)

for the title and axis I would recommend changing the position of the title:

ax.set_title("Graph Title here", va='bottom', y=1.08)

you may have to adjust the size of the figure to show the title correctly:

fig = pyplot.figure(figsize=(7,8))

for visibility of ticks you can use:

for label in ax.yaxis.get_ticklabels():
    label.set_visible(False)
for label in ax.yaxis.get_ticklabels()[::3]:
    label.set_visible(True)

overall:

import numpy
import matplotlib.pyplot as pyplot

dec = [10,20,30,40,50,60,70,80,90,80,70,60,50,40,30,20,10]
ra = [225,225,225,225,225,225,225,225,225,45,45,45,45,45,45,45,45]
n = [20,23,36,43,47,48,49,50,51,50,48,46,44,36,30,24,21]

ra = [x/180.0*3.141593 for x in ra]
fig = pyplot.figure(figsize=(7,8))
ax = fig.add_axes([0.1,0.1,0.8,0.8],polar=True)
ax.set_ylim(0,90)
ax.set_yticks(numpy.arange(0,90,10))

ax.scatter(ra,dec,c =['r' if a < 31 else 'yellow' if a < 41 else 'green' for a in n], s =40)
ax.set_title("Graph Title here", va='bottom', y=1.08)
for label in ax.yaxis.get_ticklabels():
    label.set_visible(False)
for label in ax.yaxis.get_ticklabels()[::3]:
    label.set_visible(True)
pyplot.show()