如何在 python 底图图例中显示 shapefile 标签？

Question

python底图绘制了两个内容：多线形状文件（IL_State_ln）和底图范围内一些随机点的散点图。我的兴趣是生成一个图例，该图例提供有关 shapefile 和散点的信息。目前，我只能在图例中包含点，而不能在 shapefile 中包含这些点。

检查 Basemap API documentation 没有提供任何信息，因为函数 readshapefile() 似乎没有任何 label 参数。

您能帮我像在 ArcGIS 地图中那样在图例中包含 shapefile 指示器吗？

这是我的代码：

import numpy as np    
from matplotlib import pyplot as plt
from mpl_toolkits.basemap import Basemap

fname = "DATA/GIS/IL_State_ln"

m = Basemap(llcrnrlon=-92.,llcrnrlat=36.8,urcrnrlon=-86.5,urcrnrlat=43.,
             resolution='i', projection='tmerc', lat_0 = 36.5, lon_0 = -91.8)

m.readshapefile(fname, 'mygeom')

x,y = m([-90., -91.2, -88.], [38., 37.7, 42.])
m.scatter(x,y, marker='o', label="Points")

plt.legend(loc=3)
plt.show()

我正在使用 Python 3.5、matplotlib 2.0 和底图 1.0.8。

Answer 1

创建图例条目的想法是将形状绘制为多边形，然后可以将其添加到图例中。
因此，我们将首先停用 drawbounds、m.readshapefile(fn, 'shf', drawbounds = False)。然后我们可以从 shapefile 创建一个 matplotlib.patches.Polygon 并将其添加到坐标区，plt.gca().add_artist(polygon).

然后可以使用此多边形更新图例

handles, labels = plt.gca().get_legend_handles_labels()
handles.extend([polygon])  
labels.extend(["Name of the shape"])                     
plt.legend(handles=handles, labels=labels)

下面是一些正在运行的代码，它会生成以下图像。它使用 ne_10m_admin_0_countries 文件。

from mpl_toolkits.basemap import Basemap
import matplotlib.pyplot as plt
from matplotlib.patches import Polygon
import numpy as np

m = Basemap(llcrnrlon=-10,llcrnrlat=35,urcrnrlon=35,urcrnrlat=60.,
             resolution='i', projection='tmerc', lat_0 = 48.9, lon_0 = 15.3)

m.drawcoastlines()
m.drawcountries(zorder=0, color=(.9,.9,.9), linewidth=1)

fn = r"ne_10m_admin_0_countries\ne_10m_admin_0_countries"
m.readshapefile(fn, 'shf', drawbounds = False)

#Madrid
x,y = m([-3.703889],[40.4125])
m.plot(x,y, marker="o", color="blue", label="Madrid", ls="")

# some countries
countries = ['Switzerland', 'Ireland', "Belgium"]
colors= {'Switzerland':"red", 'Ireland':"orange", 'Belgium' : "purple"}
shapes = {}
for info, shape in zip(m.shf_info, m.shf):
    if info['NAME'] in countries:
        p= Polygon(np.array(shape), True, facecolor= colors[info['NAME']], 
                   edgecolor='none', alpha=0.7, zorder=2)
        shapes.update({info['NAME'] : p})

for country in countries:
    plt.gca().add_artist(shapes[country]) 


# create legend, by first getting the already present handles, labels
handles, labels = plt.gca().get_legend_handles_labels()
# and then adding the new ones
handles.extend([shapes[c] for c in countries])  
labels.extend(countries)                     
plt.legend(handles=handles, labels=labels, framealpha=1.)

plt.show()

现在因为我们已经有了一个带有形状的多边形，为什么不通过直接将形状绘制到图例中来让图例更花哨一点。这可以按如下方式完成。

from mpl_toolkits.basemap import Basemap
import matplotlib.pyplot as plt
from matplotlib.patches import Polygon
import numpy as np

m = Basemap(llcrnrlon=-10,llcrnrlat=35,urcrnrlon=35,urcrnrlat=60.,
             resolution='i', projection='tmerc', lat_0 = 48.9, lon_0 = 15.3)

m.drawcoastlines()

fn = r"ne_10m_admin_0_countries\ne_10m_admin_0_countries"
m.readshapefile(fn, 'shf', drawbounds = False)

#Madrid
x,y = m([-3.703889],[40.4125])
m.plot(x,y, marker="o", color="blue", label="Madrid", ls="")

countries = ['Switzerland', 'Ireland', "Belgium"]
colors= {'Switzerland':"red", 'Ireland':"orange", 'Belgium' : "purple"}
shapes = {}
for info, shape in zip(m.shf_info, m.shf):
    if info['NAME'] in countries:
        p= Polygon(np.array(shape), True, facecolor= colors[info['NAME']], 
                   edgecolor='none', alpha=0.7, zorder=2)
        shapes.update({info['NAME'] : p})

for country in countries:
    plt.gca().add_artist(shapes[country]) 


class PolygonN(object):
    def legend_artist(self, legend, orig_handle, fontsize, handlebox):
        x0, y0 = handlebox.xdescent, handlebox.ydescent
        width, height = handlebox.width, handlebox.height
        aspect= height/float(width)
        verts = orig_handle.get_xy()
        minx, miny = verts[:,0].min(), verts[:,1].min()
        maxx, maxy = verts[:,0].max(), verts[:,1].max()
        aspect= (maxy-miny)/float((maxx-minx))
        nvx = (verts[:,0]-minx)*float(height)/aspect/(maxx-minx)-x0
        nvy = (verts[:,1]-miny)*float(height)/(maxy-miny)-y0

        p = Polygon(np.c_[nvx, nvy])
        p.update_from(orig_handle)
        p.set_transform(handlebox.get_transform())

        handlebox.add_artist(p)
        return p

handles, labels = plt.gca().get_legend_handles_labels()
handles.extend([shapes[c] for c in countries])  
labels.extend(countries)     
plt.legend(handles=handles, labels=labels, handleheight=3, handlelength=3, framealpha=1.,
           handler_map={Polygon: PolygonN()} )

plt.show()

如何在 python 底图图例中显示 shapefile 标签？

How to show shapefile label in python basemap legend?

python

gis

matplotlib

matplotlib-basemap