Python 空间绘图 - Cartopy 经纬度添加
本节提要：尽量符合实际应用要求的刻度与经纬度
基于很多同志询问添加经纬度办法，系统性重编了地图的经纬度添加方式。各种投影中以矩形投影PlateCarree最为方便，可以套用matplotlib.mticker的形式。在最新的0.18版本的cartopy中，虽然还不完善，但是终于能直接绘制兰勃脱下的标签了。墨卡托在官网上有示例。
一、PlateCarree投影下的两种投影方式
（1）gridlines方式
这个方式是cartopy自带的，也只能在cartopy中使用。需要引入cartopy的经纬度格式部件，然后正常添加。这种方式属于对全部投影的普适办法，但是在矩形投影上就不如matplotlib的方式。
import matplotlib.pyplot as plt
import cartopy.crs as ccrs
import cartopy.feature as cf
import numpy as np
import matplotlib.ticker as mticker
from cartopy.mpl.gridliner import LONGITUDE_FORMATTER, LATITUDE_FORMATTER
plt.rcParams['font.sans-serif']=['SimHei']
fig=plt.figure(figsize=(2,2),dpi=400)
ax=fig.add_axes([0,0,1,1],projection=ccrs.PlateCarree(central_longitude=120))
ax.add_feature(cf.LAND.with_scale('110m'))
ax.add_feature(cf.OCEAN.with_scale('110m'))
ax.add_feature(cf.COASTLINE.with_scale('110m'),lw=0.4)
ax.add_feature(cf.RIVERS.with_scale('110m'),lw=0.4)
################################################################
gl=ax.gridlines(draw_labels=True,linestyle=":",linewidth=0.3,color='k')
gl.top_labels=False #关闭上部经纬标签
gl.right_labels=False
gl.xformatter = LONGITUDE_FORMATTER #使横坐标转化为经纬度格式
gl.yformatter = LATITUDE_FORMATTER
gl.xlocator=mticker.FixedLocator(np.arange(-180,180,30))
gl.ylocator=mticker.FixedLocator(np.arange(-90,90,30))
gl.xlabel_style={'size':3}#修改经纬度字体大小
gl.ylabel_style={'size':3}
ax.spines['geo'].set_linewidth(0.5)#调节边框粗细
ax.set_title('gridlines经纬度风格',fontsize=5)
（2）matplotlib的坐标修改方式
这种方式在矩形投影中比较灵活，还可以仿制NCL风格的图片。minorticks_on这种召唤副刻度的方式比较简便，但是不能对刻度间隔进行修改。引入matplotlib.ticker的方式稍微复杂，但是能对刻度间隔进行灵活修改。
import matplotlib.pyplot as plt
import cartopy.crs as ccrs
import cartopy.feature as cf
from cartopy.mpl.ticker import LongitudeFormatter,LatitudeFormatter
plt.rcParams['font.sans-serif']=['SimHei']
fig=plt.figure(figsize=(2,2),dpi=400)
ax=fig.add_axes([0,0,1,1],projection=ccrs.PlateCarree(central_longitude=110))
ax.add_feature(cf.LAND.with_scale('110m'))
ax.add_feature(cf.OCEAN.with_scale('110m'))
ax.add_feature(cf.COASTLINE.with_scale('110m'),lw=0.4)
ax.add_feature(cf.RIVERS.with_scale('110m'),lw=0.4)
################################################################
ax.set_xticks([-180,-150,-120,-90,-60,-30,0,30,60,90,120,150,180])#指定要显示的经纬度
ax.set_yticks([-90,-60,-30,0,30,60,90])
ax.xaxis.set_major_formatter(LongitudeFormatter())#刻度格式转换为经纬度样式
ax.yaxis.set_major_formatter(LatitudeFormatter())
ax.tick_params(axis='both',which='major',labelsize=3,direction='out',length=5,width=0.3,pad=0.2,top=True,right=True)
ax.minorticks_on()
ax.tick_params(axis='both',which='minor',direction='out',width=0.3,top=True,right=True)
ax.spines['geo'].set_linewidth(0.5)#调节边框粗细
ax.set_title('Python仿制NCL风格地图',fontsize=5)
import matplotlib.pyplot as plt
import cartopy.crs as ccrs
import cartopy.feature as cf
from cartopy.mpl.ticker import LongitudeFormatter,LatitudeFormatter
import matplotlib.ticker as mticker
plt.rcParams['font.sans-serif']=['SimHei']
fig=plt.figure(figsize=(2,2),dpi=400)
ax=fig.add_axes([0,0,1,1],projection=ccrs.PlateCarree(central_longitude=110))
ax.add_feature(cf.LAND.with_scale('110m'))
ax.add_feature(cf.OCEAN.with_scale('110m'))
ax.add_feature(cf.COASTLINE.with_scale('110m'),lw=0.4)
ax.add_feature(cf.RIVERS.with_scale('110m'),lw=0.4)
################################################################
ax.set_xticks([-180,-150,-120,-90,-60,-30,0,30,60,90,120,150,180])#指定要显示的经纬度
ax.set_yticks([-90,-60,-30,0,30,60,90])
ax.xaxis.set_major_formatter(LongitudeFormatter())#刻度格式转换为经纬度样式
ax.yaxis.set_major_formatter(LatitudeFormatter())
ax.tick_params(axis='both',which='major',labelsize=3,direction='out',length=5,width=0.3,pad=0.2,top=True,right=True)
ax.xaxis.set_minor_locator(mticker.MultipleLocator(5))#刻度格式转换为经纬度样式
ax.yaxis.set_minor_locator(mticker.MultipleLocator(5))
ax.tick_params(axis='both',which='minor',direction='out',width=0.3,top=True,right=True)
ax.spines['geo'].set_linewidth(0.5)#调节边框粗细
ax.set_title('Python仿制NCL风格地图',fontsize=5)
二、兰勃脱下经纬度的添加
最开始非常不容易在矩形以外的投影下添加经纬度，要添加就只能自己造轮子。但是随着版本更新，已经支持在兰勃脱下添加标签了。有一定的缺憾，比如经纬度标签不能强制对齐。
import matplotlib.pyplot as plt
import numpy as np
import cartopy.crs as ccrs
import cartopy.feature as cf
import matplotlib.ticker as mticker
from cartopy.mpl.gridliner import LONGITUDE_FORMATTER, LATITUDE_FORMATTER
plt.rcParams['font.sans-serif']=['SimHei']
fig=plt.figure(figsize=(2,2),dpi=400)
ax=fig.add_axes([0,0,1,1],projection=ccrs.LambertConformal(central_longitude=110))
ax.add_feature(cf.LAND.with_scale('110m'))
ax.add_feature(cf.OCEAN.with_scale('110m'))
ax.add_feature(cf.COASTLINE.with_scale('110m'),lw=0.4)
ax.add_feature(cf.RIVERS.with_scale('110m'),lw=0.4)
################################################################
gl=ax.gridlines(draw_labels=True,linestyle=":",linewidth=0.3 ,x_inline=False, y_inline=False,color='k')
gl.top_labels=False #关闭上部经纬标签
gl.right_labels=False
gl.xformatter = LONGITUDE_FORMATTER #使横坐标转化为经纬度格式
gl.yformatter = LATITUDE_FORMATTER
gl.xlocator=mticker.FixedLocator(np.arange(80,140,10))
gl.ylocator=mticker.FixedLocator(np.arange(10,60,10))
gl.xlabel_style={'size':4}#修改经纬度字体大小
gl.ylabel_style={'size':4}
ax.spines['geo'].set_linewidth(0.5)#调节边框粗细
ax.set_extent([80,140,10,60],crs=ccrs.PlateCarree())
ax.set_title('LambertConformal地图',fontsize=5)
三、墨卡托下经纬度的添加
在官网上提供了墨卡托下添加经纬度标签的样例。
import matplotlib.pyplot as plt
import cartopy.feature as cf
import matplotlib.ticker as mticker
import cartopy.crs as ccrs
from cartopy.mpl.ticker import LongitudeFormatter, LatitudeFormatter,LatitudeLocator
fig=plt.figure(figsize=(2,2),dpi=400)
ax =fig.add_axes([0,0,1,1],projection=ccrs.Mercator())
ax.add_feature(cf.LAND.with_scale('110m'))
ax.add_feature(cf.OCEAN.with_scale('110m'))
ax.add_feature(cf.COASTLINE.with_scale('110m'),lw=0.4)
ax.add_feature(cf.RIVERS.with_scale('110m'),lw=0.4)
gl = ax.gridlines(crs=ccrs.PlateCarree(), draw_labels=True,
linewidth=0.3,color='k',alpha=0.5,linestyle='--')
gl.top_labels = False
gl.right_labels = False