为什么matplotlib底图不绘制地图中某些区域的颜色? [英] Why is matplotlib basemap not plotting the colours of some areas in my map?
问题描述
下面的代码应该为越南的所有州着色:
The code below is supposed to colour all the states of Vietnam:
import pandas as pd
import matplotlib.pyplot as plt
from mpl_toolkits.basemap import Basemap
fig, ax = plt.subplots(figsize=(10,20))
# create the map
map = Basemap(resolution='l', # c, l, i, h, f or None
projection='merc',
lat_0=15.95, lon_0=105.85,
llcrnrlon=102., llcrnrlat= 8.31, urcrnrlon=109.69, urcrnrlat=23.61)
# load the shapefile, use the name 'states'
map.readshapefile(r'path\to\gadm36_VNM_1', name='states', drawbounds=True)
# shapefile downloaded from http://www.gadm.org/
# collect the state names from the shapefile attributes so we can
# look up the shape obect for a state by it's name
state_names = []
for shape_dict in map.states_info:
state_names.append(shape_dict['VARNAME_1'])
ax = plt.gca() # get current axes instance
# NOR, CEN, SOU and MEK are some subdivisions I have created for the states of Vietnam
NOR = ['Lai Chau',
'Lao Cai',
'Ha Giang',
'Cao Bang',
'Dien Bien',
'Son La',
'Yen Bai',
'Tuyen Quang',
'Bac Kan',
'Lang Son',
'Thai Nguyen',
'Phu Tho',
'Vinh Phuc',
'Hoa Binh',
'Ha Noi',
'Bac Ninh',
'Hai Duong',
'Hung Yen',
'Ha Nam',
'Quang Ninh',
'Hai Phong',
'Thai Binh',
'Nam Dinh',
'Bac Giang',
'Ninh Binh']
CEN = ['Thanh Hoa',
'Nghe An',
'Ha Tinh',
'Quang Binh',
'Quang Tri',
'Thua Thien Hue',
'Da Nang']
SOU = ['Quang Nam',
'Kon Tum',
'Quang Ngai',
'Gia Lai',
'Binh Dinh',
'Dak Lak',
'Phu Yen',
'Khanh Hoa',
'Dak Nong',
'Lam Dong',
'Ninh Thuan']
MEK = ['Binh Phuoc',
'Dong Nai',
'Binh Thuan',
'Tay Ninh',
'Binh Duong',
'Dong Nai',
'Ba Ria - Vung Tau',
'Ho Chi Minh',
'Long An',
'An Giang',
'Dong Thap',
'Tien Giang',
'Kien Giang',
'Can Tho',
'Vinh Long',
'Ben Tre',
'Hau Giang',
'Tra Vinh',
'Soc Trang',
'Bac Lieu',
'Ca Mau']
# Define the colours to be used to colour the states
from matplotlib import cm
from numpy import linspace
start = 0.5
stop = 1.0
number_of_lines= 4
cm_subsection = linspace(start, stop, number_of_lines)
cm_subsection[0] = cm_subsection[0]*4
cm_subsection[1] = cm_subsection[1]*0.6
cm_subsection[2] = cm_subsection[2]*0.8
cm_subsection[3] = cm_subsection[3]*0.1
colors = [ cm.Blues(x) for x in cm_subsection ]
for state in NOR:
seg = map.states[state_names.index(state)]
poly = Polygon(seg, facecolor=colors[0], edgecolor=colors[0])
ax.add_patch(poly)
for state in CEN:
seg = map.states[state_names.index(state)]
poly = Polygon(seg, facecolor=colors[1], edgecolor=colors[1])
ax.add_patch(poly)
for state in SOU:
seg = map.states[state_names.index(state)]
poly = Polygon(seg, facecolor=colors[2], edgecolor=colors[2])
ax.add_patch(poly)
for state in MEK:
seg = map.states[state_names.index(state)]
poly = Polygon(seg, facecolor=colors[3], edgecolor=colors[3])
ax.add_patch(poly)
import matplotlib.patches as mpatches
NOR_patch = mpatches.Patch(color=colors[0], label='Rate: 34.85%')
CEN_patch = mpatches.Patch(color=colors[1], label='Rate: 25.61%')
SOU_patch = mpatches.Patch(color=colors[2], label='Rate: 32.66%')
MEK_patch = mpatches.Patch(color=colors[3], label='Rate: 20.02%')
plt.legend(handles=[NOR_patch, CEN_patch, SOU_patch, MEK_patch])
plt.show()
但这会生成下面的地图，其中有些州即使在州名和分区中也没有显示颜色:
But this produces the map below, where some of the states are not coloured even though they are present in the state names and in the subdivisions:
实际上，如果我尝试为列表中不存在其名称的州上色，则会引发错误:
In fact, if I try to colour a state whose name is not present in the lists, it throws an error:
MEK.append('ABCDE')
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
<ipython-input-619-a89da62a0831> in <module>()
134
135 for state in MEK:
--> 136 seg = map.states[state_names.index(state)]
137 poly = Polygon(seg, facecolor=colors[3], edgecolor=colors[3])
138 ax.add_patch(poly)
ValueError: 'ABCDE' is not in list
因此，很明显，列表中存在未着色的状态，因为我没有收到任何错误.那么，这是怎么回事?
So, clearly the states that are not colored are present in the list, as I'm not getting any error. So, what's going on?
编辑:令我惊讶的是，几乎所有未着色的州在现实世界中都至少与海洋有部分边界.这6个例外情况以红色突出显示在下面:
It just struck me that almost all the states that aren’t coloured share at least some part of their border with sea/ocean in the real world. The 6 exceptions are highlighted in red below:
现在，这很有趣！可能与这个问题有关吗?如果是，那是什么?又为什么呢?为何存在这6个例外?
Now that’s very interesting! Could it have anything to do with the issue? If yes, what? And why? And why do those 6 exceptions exist?
在绘制菲律宾地图时，我得到类似的结果:
EDIT 2: I get similar results when drawing the map of Philippines:
推荐答案
在shapefiles中，一个国家/地区/任何地方，都可以分为几个线段.我不知道为什么，但是要正确绘制形状，您需要使用所有必要的线段.实际上，在 shapefile的底图文档中，有一个填充多边形"示例'，如何正确执行此操作.我根据您的用例调整了他们的示例.这可能不是最理想的解决方案，但它似乎可以工作.
In shapefiles, a country/province/whatever, may be broken down into several line segments. Why that is, I don't know, but in order to plot the shape correctly, you need to use all the necessary segments. Actually, in the Basemap documentation for shapefiles there is an example under 'filling polygons', how to do this correctly. I adapted their example to your use case. It's probably not the most optimal solution, but it seems to work.
import pandas as pd
import matplotlib.pyplot as plt
from mpl_toolkits.basemap import Basemap
from matplotlib import patches as mpatches
from matplotlib import cm
from numpy import linspace
import matplotlib.patches as mpatches
from matplotlib.collections import PatchCollection
fig, ax = plt.subplots(figsize=(4,8))
# create the map
map = Basemap(resolution='l', # c, l, i, h, f or None
projection='merc',
lat_0=15.95, lon_0=105.85,
llcrnrlon=102., llcrnrlat= 8.31, urcrnrlon=109.69, urcrnrlat=23.61)
# load the shapefile, use the name 'states'
map.readshapefile(r'shapefiles/gadm36_VNM_1', name='states', drawbounds=True)
# shapefile downloaded from http://www.gadm.org/
# collect the state names from the shapefile attributes so we can
# look up the shape obect for a state by it's name
state_names = []
for shape_dict in map.states_info:
state_names.append(shape_dict['VARNAME_1'])
ax = plt.gca() # get current axes instance
# NOR, CEN, SOU and MEK are some subdivisions I have created for the states of Vietnam
NOR = ['Lai Chau',
'Lao Cai',
'Ha Giang',
'Cao Bang',
'Dien Bien',
'Son La',
'Yen Bai',
'Tuyen Quang',
'Bac Kan',
'Lang Son',
'Thai Nguyen',
'Phu Tho',
'Vinh Phuc',
'Hoa Binh',
'Ha Noi',
'Bac Ninh',
'Hai Duong',
'Hung Yen',
'Ha Nam',
'Quang Ninh',
'Hai Phong',
'Thai Binh',
'Nam Dinh',
'Bac Giang',
'Ninh Binh']
CEN = ['Thanh Hoa',
'Nghe An',
'Ha Tinh',
'Quang Binh',
'Quang Tri',
'Thua Thien Hue',
'Da Nang']
SOU = ['Quang Nam',
'Kon Tum',
'Quang Ngai',
'Gia Lai',
'Binh Dinh',
'Dak Lak',
'Phu Yen',
'Khanh Hoa',
'Dak Nong',
'Lam Dong',
'Ninh Thuan']
MEK = ['Binh Phuoc',
'Dong Nai',
'Binh Thuan',
'Tay Ninh',
'Binh Duong',
'Dong Nai',
'Ba Ria - Vung Tau',
'Ho Chi Minh',
'Long An',
'An Giang',
'Dong Thap',
'Tien Giang',
'Kien Giang',
'Can Tho',
'Vinh Long',
'Ben Tre',
'Hau Giang',
'Tra Vinh',
'Soc Trang',
'Bac Lieu',
'Ca Mau']
# Define the colours to be used to colour the states
start = 0.5
stop = 1.0
number_of_lines= 4
cm_subsection = linspace(start, stop, number_of_lines)
cm_subsection[0] = cm_subsection[0]*4
cm_subsection[1] = cm_subsection[1]*0.6
cm_subsection[2] = cm_subsection[2]*0.8
cm_subsection[3] = cm_subsection[3]*0.1
colors = [ cm.Blues(x) for x in cm_subsection ]
##collecting the line segments for the provinces:
patches = {state: [] for state in NOR+CEN+SOU+MEK}
for info, shape in zip(map.states_info, map.states):
for state in NOR+CEN+SOU+MEK:
if info['VARNAME_1'] == state:
patches[state].append(mpatches.Polygon(
shape, True,
))
##coloring the the provinces by group:
for state in NOR:
ax.add_collection(PatchCollection(
patches[state], facecolor = colors[0], edgecolor=colors[0]
))
for state in CEN:
ax.add_collection(PatchCollection(
patches[state], facecolor = colors[1], edgecolor=colors[1]
))
for state in SOU:
ax.add_collection(PatchCollection(
patches[state], facecolor = colors[2], edgecolor=colors[2]
))
for state in MEK:
ax.add_collection(PatchCollection(
patches[state], facecolor = colors[3], edgecolor=colors[3]
))
NOR_patch = mpatches.Patch(color=colors[0], label='Rate: 34.85%')
CEN_patch = mpatches.Patch(color=colors[1], label='Rate: 25.61%')
SOU_patch = mpatches.Patch(color=colors[2], label='Rate: 32.66%')
MEK_patch = mpatches.Patch(color=colors[3], label='Rate: 20.02%')
plt.legend(handles=[NOR_patch, CEN_patch, SOU_patch, MEK_patch])
plt.show()
结果看起来像预期的那样:
The result looks as expected:
请注意，我只能在Python 3.6下测试代码，因此可能需要进行一些调整.希望这会有所帮助.
Note that I could only test the code under Python 3.6, so there might be some adjustments necessary. Hope this helps.
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