Question

下面的代码应该为越南的所有州着色：

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()

但这会产生下面的地图，其中有些州即使在州名和分区中也没有显示颜色：

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：

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，显然没有颜色的状态出现在列表中，因为我没有收到任何错误。那么，这是怎么回事？

编辑：令我感到惊讶的是，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：

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？为什么存在这6个例外？

编辑2： 在绘制菲律宾地图时，我得到类似的结果：

Answer 1

在shapefiles中，一个国家/地区/任何地方都可以细分为多个线段。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Basemap documentation for shapefiles中有一个“填充多边形”下的示例，说明如何正确执行此操作。我将他们的示例适应您的用例。这可能不是最理想的解决方案，但它似乎有效。

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：

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。

为什么matplotlib底图不绘制地图中某些区域的颜色？

1 个答案: