如何在Python Basemap图例中显示Shapefile标签？

Question

如何在Python Basemap图例中显示Shapefile标签？

pythonmatplotlibgismatplotlib-basemap

3

Python Basemap有两个内容：一个是多线形状文件（IL_State_ln），另一个是随机点的散点图。我想生成一个图例，其中包含关于形状文件和散点的信息。目前，我只能在图例中包括散点，而不能包括形状文件。

查看Basemap API文档Basemap API documentation并没有提供任何信息，因为函数readshapefile()似乎没有"label"参数。

请帮助我像ArcGIS地图一样将形状文件指示符包含在图例中。

以下是我的代码：

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basemap 1.0.8。

- SereneWizard

1个回答

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- ImportanceOfBeingErnest · Accepted Answer

创建图例条目的想法是绘制多边形形状，然后将其添加到图例中。

因此，我们首先需要停用drawbounds，m.readshapefile(fn, 'shf', drawbounds = False)。然后我们可以从形状文件创建一个matplotlib.patches.Polygon并将其添加到轴上plt.gca().add_artist(polygon)。

然后可以使用该多边形更新图例。

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

以下是一些示例代码，它会生成如下图像。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()

现在我们已经有了一个形状的多边形，为什么不将形状直接绘制到图例中，使其更加华丽。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()