Basemap: Get all data points on colorbar which each point refelecting the ploted color

Question

I have a dataset, containing different types of trees in numerical i.e

Types = 4,8,9,10,13,15,19,33

I am plotting these types on a scatter plot, each type being represented by a different color. I can’t figure out a way for the color bar to represent the data correctly. So that it looks like this.

The color bar ticks should only represent the data plotted with each color representing a type. i.e

Green = 4
Orange = 8
etc

The plot below is my failed attempt at doing this. The colorbar ticks do not represent the vegetation plotted but a range.

fig = plt.figure()
plt.figure(figsize=(25,10))
m=Basemap(projection='mill',llcrnrlat=25,llcrnrlon=-130,urcrnrlat=49,urcrnrlon=-104.5,resolution='l')
m.drawcoastlines()
m.drawcountries()
m.drawstates()
x,y=m(list(Y60['col']),list(Y60['row']))
m.scatter(x,y,c=Y60['potveg'],s=Y60['potveg']*5,cmap='Dark2')
cbar=plt.color bar()

Thanks

Asked By: Jared Kodero

||

Source

Answer 1

My answer focuses on the steps to create the legend. Read the comments in the code for explanation.

import matplotlib.pyplot as plt

# Each item of legends requires 3 propereties: color/label_text/marker_shape
colors = ["green", "orange", "purple", "red", "lightgreen", "gray"]
texts = ["4", "9", "13", "15", "19", "33"]
markers = ["o", "o", "o", "o", "o", "o"]
len0 = len(colors)

# Points' locations and attributes
xs = [3,2,4,5,4,2,7,3]
ys = [41,12,32,15,35,21,23,43]
colors1 = ["green", "orange", "purple", "red", "lightgreen", "gray", "green", "orange"]
texts1 = ["4", "9", "13", "15", "19", "33", "4", "9"]
markers1 = ["o", "o", "o", "o", "o", "o", "o", "o"]
sizes1 = [8,16,9,12,7,4,10,6]
len1 = len(xs)

# Plot `none` data point and 
#  save the output patches objects for legend making
patches0 = [ plt.plot([],[], marker=markers[i], ms=8, ls="", mec=None, color=colors[i], 
          label="{:s}".format(texts[i]) )[0]
          for i in range(len0) ]
# Plot point data
# Demo data is used here
for i in range(len1):
    plt.plot(xs[i], ys[i], marker=markers1[i], ms=sizes1[i], color=colors1[i])

# Plot legend in the upper-right corner
plt.legend(handles=patches0, bbox_to_anchor=(1, 1), title="Potveg", 
                   loc='upper right', ncol=1, facecolor="lightgray", numpoints=1 )
plt.show()

Edit1

Since the data has categories and quantities information to render on the plot, my answer is not complete without handling both of them.

The code to produce 2 legends on a single plot is not straight forward as one may think.

import matplotlib.pyplot as plt

# For `Categories` symbol
# ----------------
# Each item of legends requires 3 propereties: color/label_text/marker_shape
color_V = ["green", "orange", "purple", "red", "lightgreen", "gray"]
text_V = ["4", "9", "13", "15", "19", "33"]
marker_V = ["o", "o", "o", "o", "o", "o"]
len_V = len(color_V)

# For `Size/quantities` symbol
# --------------------
color_S = ["gray", "gray", "gray", "gray"]
sizes_S = [4, 8, 12, 16]         #increasing values ...
text_S = ["4", "8", "12", "16"]  # cover `sizes1` below
marker_S = ["o", "o", "o", "o"]  #use disk shape
len_S = len(color_S)

# Data locations and attributes
xs = [3,2,4,5,4,2,7,3]
ys = [41,12,32,15,35,21,23,43]
colors1 = ["green", "orange", "purple", "red", "lightgreen", "gray", "green", "orange"]
texts1 = ["4", "9", "13", "15", "19", "33", "4", "9"]
markers1 = ["o", "o", "o", "o", "o", "o", "o", "o"]
sizes1 = [8,16,9,12,7,4,10,6]
len1 = len(xs)

# Plot `none` data point and 
#  save the output patches objects for legend making
patches_V = [ plt.plot([],[], marker=marker_V[i], ms=8, ls="", color=color_V[i], 
          label="{:s}".format(text_V[i]) )[0] 
          for i in range(len_V) ]

# Do it again for another legend
patches_S = [ plt.plot([],[], marker=marker_S[i], ms=sizes_S[i], ls="", 
        color=color_S[i], 
        label="{:s}".format(text_S[i]) )[0] for i in range(len_S) ]

# Plot point data
# Demo data is used here
for i in range(len1):
    plt.plot(xs[i], ys[i], marker=markers1[i], ms=sizes1[i], color=colors1[i])

# Plot 1st legend in the upper-right corner
first_legend = plt.legend(handles=patches_V, bbox_to_anchor=(1, 1), title="Categories", 
                   loc='upper right', ncol=1, facecolor="lightgray", numpoints=1 )

# Need to freeze first legend to enable addition of the second legend by ...
# Add the legend manually to the current Axes
plt.gca().add_artist(first_legend)

# Then we can add the second legend normally
plt.legend(handles=patches_S, bbox_to_anchor=(0, 1), title="Sizes", 
                   loc='upper left', ncol=1, facecolor="lightgray", numpoints=1 )


plt.show()

Answered By: swatchai

Basemap: Get all data points on colorbar which each point refelecting the ploted color

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