Python绘图：在地图上添加小地图
在科学研究中，我们经常需要在大范围的地图上添加小地图来突出显示研究区域。本文将介绍如何使用Python的cartopy和matplotlib库来实现这一功能。
基本概念
什么是小地图（Inset Map）
小地图是一个嵌入在主地图中的小型地图，通常用于：
- 显示研究区域位置：在大范围地图中标出具体研究区域
- 提供地理背景：为读者提供地理位置的参考
- 增强地图可读性：帮助读者更好地理解空间关系
应用场景
- 科学论文：在研究区域图中添加位置示意图
- 数据报告：在区域分析图中提供全局视角
- 演示文稿：增强地图的表达效果
技术准备
所需库
import matplotlib.pyplot as plt
import cartopy.crs as ccrs
import cartopy.feature as cfeature
import numpy as np
from cartopy.mpl.gridliner import LONGITUDE_FORMATTER, LATITUDE_FORMATTER
import matplotlib.patches as patches
from matplotlib.patches import Rectangle
import cartopy.io.shapereader as shpreader
安装依赖
pip install matplotlib cartopy numpy
# 如果需要额外的地图数据
pip install cartopy[plotting]
基础实现
1. 简单的小地图示例
def create_basic_inset_map():
"""
创建基础的小地图示例
"""
# 创建主图
fig = plt.figure(figsize=(12, 8))
# 主地图 - 中国东部区域
ax_main = fig.add_subplot(111, projection=ccrs.PlateCarree())
ax_main.set_extent([105, 125, 25, 45], ccrs.PlateCarree())
# 添加地图特征
ax_main.add_feature(cfeature.COASTLINE, linewidth=0.8)
ax_main.add_feature(cfeature.BORDERS, linewidth=0.6)
ax_main.add_feature(cfeature.RIVERS, alpha=0.6)
ax_main.add_feature(cfeature.LAKES, alpha=0.6)
# 添加网格
gl = ax_main.gridlines(draw_labels=True, alpha=0.5)
gl.top_labels = False
gl.right_labels = False
gl.xformatter = LONGITUDE_FORMATTER
gl.yformatter = LATITUDE_FORMATTER
# 创建小地图 - 显示整个中国
ax_inset = fig.add_axes([0.02, 0.65, 0.3, 0.3],
projection=ccrs.PlateCarree())
ax_inset.set_extent([70, 140, 10, 55], ccrs.PlateCarree())
# 添加小地图特征
ax_inset.add_feature(cfeature.COASTLINE, linewidth=0.5)
ax_inset.add_feature(cfeature.BORDERS, linewidth=0.4)
ax_inset.add_feature(cfeature.LAND, color='lightgray', alpha=0.5)
ax_inset.add_feature(cfeature.OCEAN, color='lightblue', alpha=0.3)
# 在小地图上标出主地图的范围
rect = patches.Rectangle((105, 25), 20, 20,
linewidth=2, edgecolor='red',
facecolor='none', transform=ccrs.PlateCarree())
ax_inset.add_patch(rect)
# 添加标题
ax_main.set_title('中国东部地区详细地图', fontsize=14, pad=20)
plt.tight_layout()
return fig, ax_main, ax_inset
# 创建地图
fig, ax_main, ax_inset = create_basic_inset_map()
plt.show()
2. 高级小地图功能
class InsetMapCreator:
"""
小地图创建器类
"""
def __init__(self, figsize=(12, 10)):
self.fig = plt.figure(figsize=figsize)
self.ax_main = None
self.ax_inset = None
def create_main_map(self, extent, projection=ccrs.PlateCarree()):
"""
创建主地图
Parameters:
-----------
extent : list
地图范围 [lon_min, lon_max, lat_min, lat_max]
projection : cartopy projection
地图投影
"""
self.ax_main = self.fig.add_subplot(111, projection=projection)
self.ax_main.set_extent(extent, ccrs.PlateCarree())
# 添加基本地图特征
self.ax_main.add_feature(cfeature.COASTLINE, linewidth=1.0)
self.ax_main.add_feature(cfeature.BORDERS, linewidth=0.8)
self.ax_main.add_feature(cfeature.RIVERS, alpha=0.6)
self.ax_main.add_feature(cfeature.LAKES, alpha=0.6)
self.ax_main.add_feature(cfeature.LAND, color='lightgray', alpha=0.3)
self.ax_main.add_feature(cfeature.OCEAN, color='lightblue', alpha=0.3)
return self.ax_main
def add_inset_map(self, position, inset_extent,
main_extent=None, projection=ccrs.PlateCarree()):
"""
添加小地图
Parameters:
-----------
position : list
小地图位置 [x, y, width, height] (相对坐标)
inset_extent : list
小地图显示范围
main_extent : list
主地图范围（用于在小地图上标注）
projection : cartopy projection
小地图投影
"""
self.ax_inset = self.fig.add_axes(position, projection=projection)
self.ax_inset.set_extent(inset_extent, ccrs.PlateCarree())
# 添加小地图特征
self.ax_inset.add_feature(cfeature.COASTLINE, linewidth=0.5)
self.ax_inset.add_feature(cfeature.BORDERS, linewidth=0.4)
self.ax_inset.add_feature(cfeature.LAND, color='lightgray', alpha=0.5)
self.ax_inset.add_feature(cfeature.OCEAN, color='lightblue', alpha=0.3)
# 标注主地图范围
if main_extent:
lon_min, lon_max, lat_min, lat_max = main_extent
rect = patches.Rectangle((lon_min, lat_min),
lon_max - lon_min,
lat_max - lat_min,
linewidth=2, edgecolor='red',
facecolor='red', alpha=0.3,
transform=ccrs.PlateCarree())
self.ax_inset.add_patch(rect)
return self.ax_inset
def add_gridlines(self, ax, **kwargs):
"""
添加网格线
"""
gl = ax.gridlines(draw_labels=True, alpha=0.5, **kwargs)
gl.top_labels = False
gl.right_labels = False
gl.xformatter = LONGITUDE_FORMATTER
gl.yformatter = LATITUDE_FORMATTER
return gl
实际应用示例
示例1：上海及周边地区
def create_shanghai_map():
"""
创建上海及周边地区地图，带小地图显示位置
"""
creator = InsetMapCreator(figsize=(14, 10))
# 主地图：上海及周边详细地图
main_extent = [120, 122.5, 30.5, 32]
ax_main = creator.create_main_map(main_extent)
# 添加网格
creator.add_gridlines(ax_main)
# 添加数据点（示例）
shanghai_lon, shanghai_lat = 121.47, 31.23
ax_main.plot(shanghai_lon, shanghai_lat, 'ro', markersize=8,
transform=ccrs.PlateCarree(), label='上海市中心')
# 小地图：显示在中国的位置
inset_extent = [70, 140, 10, 55]
ax_inset = creator.add_inset_map([0.02, 0.65, 0.3, 0.3],
inset_extent, main_extent)
# 添加标题和标签
ax_main.set_title('上海及周边地区详细地图', fontsize=16, pad=20)
ax_main.legend(loc='upper right')
return creator.fig
# 创建地图
fig = create_shanghai_map()
plt.show()
示例2：多个小地图
def create_multi_inset_map():
"""
创建包含多个小地图的复合地图
"""
fig = plt.figure(figsize=(16, 12))
# 主地图：中国东部
ax_main = fig.add_subplot(2, 2, (1, 3), projection=ccrs.PlateCarree())
ax_main.set_extent([105, 125, 25, 45], ccrs.PlateCarree())
# 添加主地图特征
ax_main.add_feature(cfeature.COASTLINE, linewidth=1.0)
ax_main.add_feature(cfeature.BORDERS, linewidth=0.8)
ax_main.add_feature(cfeature.LAND, color='lightgray', alpha=0.3)
ax_main.add_feature(cfeature.OCEAN, color='lightblue', alpha=0.3)
# 小地图1：北京周边
ax_beijing = fig.add_subplot(2, 2, 2, projection=ccrs.PlateCarree())
ax_beijing.set_extent([115, 118, 39, 41], ccrs.PlateCarree())
ax_beijing.add_feature(cfeature.COASTLINE, linewidth=0.5)
ax_beijing.add_feature(cfeature.BORDERS, linewidth=0.4)
ax_beijing.set_title('北京地区')
# 小地图2：上海周边
ax_shanghai = fig.add_subplot(2, 2, 4, projection=ccrs.PlateCarree())
ax_shanghai.set_extent([120, 122.5, 30.5, 32], ccrs.PlateCarree())
ax_shanghai.add_feature(cfeature.COASTLINE, linewidth=0.5)
ax_shanghai.add_feature(cfeature.BORDERS, linewidth=0.4)
ax_shanghai.set_title('上海地区')
# 在主地图上标注两个区域
# 北京区域
rect_beijing = patches.Rectangle((115, 39), 3, 2,
linewidth=2, edgecolor='blue',
facecolor='blue', alpha=0.3,
transform=ccrs.PlateCarree())
ax_main.add_patch(rect_beijing)
# 上海区域
rect_shanghai = patches.Rectangle((120, 30.5), 2.5, 1.5,
linewidth=2, edgecolor='red',
facecolor='red', alpha=0.3,
transform=ccrs.PlateCarree())
ax_main.add_patch(rect_shanghai)
ax_main.set_title('中国东部地区及重点城市', fontsize=16, pad=20)
plt.tight_layout()
return fig
# 创建多小地图
fig = create_multi_inset_map()
plt.show()
高级技巧
1. 连接线
def add_connection_lines(fig, ax_main, ax_inset, main_extent):
"""
在主地图和小地图之间添加连接线
"""
from matplotlib.patches import ConnectionPatch
# 计算连接点
lon_min, lon_max, lat_min, lat_max = main_extent
# 主地图上的点
x1, y1 = ax_main.projection.transform_point(lon_min, lat_min,
ccrs.PlateCarree())
# 小地图上的点
x2, y2 = ax_inset.projection.transform_point(lon_min, lat_min,
ccrs.PlateCarree())
# 创建连接线
con = ConnectionPatch((x1, y1), (x2, y2), "data", "data",
axesA=ax_main, axesB=ax_inset,
color="red", linewidth=1, alpha=0.7)
ax_inset.add_artist(con)
return con
2. 自定义样式
def customize_map_style(ax, style='scientific'):
"""
自定义地图样式
"""
if style == 'scientific':
# 科学论文风格
ax.add_feature(cfeature.COASTLINE, linewidth=0.8, color='black')
ax.add_feature(cfeature.BORDERS, linewidth=0.6, color='gray')
ax.add_feature(cfeature.LAND, color='white')
ax.add_feature(cfeature.OCEAN, color='lightblue', alpha=0.5)
elif style == 'presentation':
# 演示文稿风格
ax.add_feature(cfeature.COASTLINE, linewidth=1.2, color='darkblue')
ax.add_feature(cfeature.BORDERS, linewidth=0.8, color='darkgray')
ax.add_feature(cfeature.LAND, color='lightgreen', alpha=0.3)
ax.add_feature(cfeature.OCEAN, color='lightblue', alpha=0.7)
elif style == 'minimal':
# 简约风格
ax.add_feature(cfeature.COASTLINE, linewidth=0.5, color='black')
ax.add_feature(cfeature.BORDERS, linewidth=0.3, color='gray')
ax.add_feature(cfeature.LAND, color='white')
ax.add_feature(cfeature.OCEAN, color='white')
性能优化
1. 地图数据缓存
class CachedMapCreator:
"""
带缓存的地图创建器
"""
def __init__(self):
self.cached_features = {}
def get_cached_feature(self, feature_name, resolution='50m'):
"""
获取缓存的地图特征
"""
cache_key = f"{feature_name}_{resolution}"
if cache_key not in self.cached_features:
if feature_name == 'coastline':
self.cached_features[cache_key] = cfeature.COASTLINE.with_scale(resolution)
elif feature_name == 'borders':
self.cached_features[cache_key] = cfeature.BORDERS.with_scale(resolution)
# 添加更多特征...
return self.cached_features[cache_key]
2. 分辨率控制
def create_optimized_map(main_extent, inset_extent,
main_resolution='50m', inset_resolution='110m'):
"""
创建优化的地图（不同分辨率）
"""
fig = plt.figure(figsize=(12, 8))
# 主地图使用高分辨率
ax_main = fig.add_subplot(111, projection=ccrs.PlateCarree())
ax_main.set_extent(main_extent, ccrs.PlateCarree())
ax_main.add_feature(cfeature.COASTLINE.with_scale(main_resolution))
ax_main.add_feature(cfeature.BORDERS.with_scale(main_resolution))
# 小地图使用低分辨率
ax_inset = fig.add_axes([0.02, 0.65, 0.3, 0.3],
projection=ccrs.PlateCarree())
ax_inset.set_extent(inset_extent, ccrs.PlateCarree())
ax_inset.add_feature(cfeature.COASTLINE.with_scale(inset_resolution))
ax_inset.add_feature(cfeature.BORDERS.with_scale(inset_resolution))
return fig, ax_main, ax_inset
总结
通过本文的介绍，我们学习了如何使用Python创建带有小地图的地图可视化：
- 基础概念：了解了小地图的作用和应用场景
- 基本实现：掌握了使用cartopy创建小地图的基本方法
- 高级功能：学习了如何创建复杂的多小地图布局
- 样式定制：了解了如何自定义地图样式
- 性能优化：学习了提高地图渲染效率的方法
小地图是科学可视化中的重要工具，合理使用可以大大提升地图的信息传达效果。在实际应用中，需要根据具体需求选择合适的位置、大小和样式。
参考资源
希望这篇文章对您在Python地图可视化方面有所帮助！