Python Cartopy添加Shapefile后图例不显示问题求助

你遇到的问题根源在于ax.add_geometries()方法不会将要素的label参数关联到matplotlib的图例系统，导致调用ax.legend()时找不到带标签的绘图元素，最终出现空白图例和报错。

以下是两种可行的解决方法：

方案一：使用ax.add_feature()（推荐） #

Cartopy的add_feature()方法是专门为添加地理要素设计的，会自动处理图例标签的关联，代码更简洁：

import matplotlib.pyplot as plt
import cartopy.crs as ccrs
import cartopy.feature as cfeature

fig = plt.figure(figsize=(10, 8))
ax = fig.add_subplot(1, 1, 1, projection=ccrs.PlateCarree())

# 定义并添加陆地要素
land_feature = cfeature.NaturalEarthFeature(
    'physical', 'land', '50m',
    edgecolor='black', facecolor='gray',
    label='Land'
)
ax.add_feature(land_feature)

# 定义并添加海洋要素
ocean_feature = cfeature.NaturalEarthFeature(
    'physical', 'ocean', '50m',
    edgecolor='face', facecolor='blue',
    label='Ocean'
)
ax.add_feature(ocean_feature)

ax.set_title('Map with Shapefile Legend')
ax.gridlines()
ax.legend(loc='lower left')

plt.show()

方案二：手动创建图例条目 #

如果必须使用ax.add_geometries()，可以通过matplotlib的Patch对象手动构建图例元素：

import matplotlib.pyplot as plt
import cartopy.crs as ccrs
import cartopy.feature as cfeature
from matplotlib.patches import Patch

fig = plt.figure(figsize=(10, 8))
ax = fig.add_subplot(1, 1, 1, projection=ccrs.PlateCarree())

# 添加陆地和海洋几何要素
ax.add_geometries(
    cfeature.NaturalEarthFeature('physical', 'land', '50m').geometries(),
    ccrs.PlateCarree(),
    facecolor='gray', edgecolor='black'
)
ax.add_geometries(
    cfeature.NaturalEarthFeature('physical', 'ocean', '50m').geometries(),
    ccrs.PlateCarree(),
    facecolor='blue', edgecolor='face'
)

# 手动创建图例补丁
legend_patches = [
    Patch(facecolor='gray', edgecolor='black', label='Land'),
    Patch(facecolor='blue', edgecolor='face', label='Ocean')
]

ax.set_title('Map with Shapefile Legend')
ax.gridlines()
# 传入手动创建的补丁生成图例
ax.legend(handles=legend_patches, loc='lower left')

plt.show()

内容的提问来源于stack exchange，提问作者Rony Golder