[英]Adding value labels on a cartopy choropleth map
我正在使用 cartopy 創建一些 choropleth 地圖,並想添加一個附加功能:帶有與每個國家/地區的 choropleth 相關聯的數值的標簽。
我想我可以在正確的坐標上一個一個地手動添加每個標簽,但我相信有一種更快、更通用和更具可擴展性的方法來做到這一點。 我花了相當多的時間進行研究,但還沒有找到任何方便的解決方案,因此將非常感謝任何幫助。
這是我用來繪制等值線圖的函數:
def choropleth(ax, countries, geo_dict, cmap_name):
"""
Plots a choropleth map of selected countries using the values in geo_dict
as a base for the colormap
ax: matplotlib axes on which the cloropleth is drawn
countries: a list of records extracted from a shp file representing the
regions to be mapped
geo_dict: a dictionary in which the keys are ISO alpha-2 country codes and
the values the relevant data for the choropleth
cmap_name: a string with the name of the colormap to be used
"""
# value normalization for the color map
values = [geo_dict[[c.attributes['ISO_A2']][0]] for c in countries]
norm = Normalize(vmin=min(values), vmax=max(values))
cmap = plt.cm.get_cmap(cmap_name) # add ',n' to limit choropleth categories
for c in countries:
v = geo_dict[c.attributes['ISO_A2']]
sp = ShapelyFeature(c.geometry, crs,
edgecolor='k',
linewidth=0.3,
zorder = 2,
facecolor=cmap(norm(v)))
ax.add_feature(sp)
sm = plt.cm.ScalarMappable(cmap=cmap,norm=norm)
sm._A = []
plt.colorbar(sm,ax=ax)
Q : 如何為每個國家添加標簽?
簡短回答:就在ax.add_feature()
,使用ax.annotate()
。 您需要獲取 c.geometry 的質心作為 annotate 的參數。
答:您的代碼缺少繪制標簽的正確命令。 在這種情況下最合適的是ax.annotate()
,它應該放在ax.add_feature()
。 需要的參數包括:
crs
)這是應該將標簽添加到每個國家/地區的質心位置的代碼片段:
# ... other lines of code above here
ax.add_feature(sp) # existing code
# my code follows
pnt = c.geometry.centroid
anno = c.attributes['ISO_A2'] # 'name' is also possible
# `Axes CRS` is taken from: ax.projection
# `Data CRS` is taken as `crs`
ax.annotate(anno, ax.projection.transform_point(pnt.x, pnt.y, crs))
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