投影法による面積のひずみ
メルカトル図法では面積は正しく表示されない.これは正積図法ではない.
In[1]:=
![Click for copyable input](assets.ja/area-distortion-by-a-projection/In_28.png)
GeoProjectionData["Mercator", "EqualArea"]
Out[1]=
![](assets.ja/area-distortion-by-a-projection/O_19.png)
アフリカの面積はグリーンランドの面積の14倍を超える大きさである.
In[2]:=
![Click for copyable input](assets.ja/area-distortion-by-a-projection/In_29.png)
GeoArea[Entity["GeographicRegion", "Africa"]]/
GeoArea[Entity["Country", "Greenland"]]
Out[2]=
![](assets.ja/area-distortion-by-a-projection/O_20.png)
しかし,メルカトル図法では,アフリカとグリーンランドがほとんど同じ大きさに見える.
In[3]:=
![Click for copyable input](assets.ja/area-distortion-by-a-projection/In_30.png)
GeoGraphics[{GeoStyling[Green],
Polygon[Entity["Country", "Greenland"]], GeoStyling[Red],
Polygon[Entity["GeographicRegion", "Africa"]]},
GeoProjection -> "Mercator", GeoRange -> "World",
GeoBackground -> "Satellite"]
Out[3]=
![](assets.ja/area-distortion-by-a-projection/O_21.png)
モルワイデ図法のような正積図法を使うと,相対的な大きさがより適切に表せる.
In[4]:=
![Click for copyable input](assets.ja/area-distortion-by-a-projection/In_31.png)
GeoProjectionData["Mollweide", "EqualArea"]
Out[4]=
![](assets.ja/area-distortion-by-a-projection/O_22.png)
In[5]:=
![Click for copyable input](assets.ja/area-distortion-by-a-projection/In_32.png)
GeoGraphics[{GeoStyling[Green],
Polygon[Entity["Country", "Greenland"]], GeoStyling[Red],
Polygon[Entity["GeographicRegion", "Africa"]]},
GeoProjection -> "Mollweide", GeoRange -> "World",
GeoBackground -> "Satellite"]
Out[5]=
![](assets.ja/area-distortion-by-a-projection/O_23.png)