如何将 geopandas crs 单位转换为米 ^ 2? [英] How can I convert geopandas crs units to meters^2?

问题描述

我正在使用 geopandas，我正在尝试获取我上传的 shapefile 的区域，但我不确定 .area 属性结果的测量单位是什么.这是我的代码:

I'm using geopandas, and I'm trying to get the areas of the shapefile I uploaded, but I'm unsure of what the unit of measurement is for the result of the .area attribute. Here is my code:

water = gp.read_file("/Users/user/Downloads/tlgdb_2020_a_us_areawater.gdb")
lakeSup = water.loc[water['FULLNAME'].str.contains('Lk Superior', na=False)]
lakeSup = lakeSup.to_crs(epsg=4269)
lakeSup['area'] = lakeSup.area
print(lakeSup.head(10))

哪些输出

       ANSICODE  ...      area
233938     None  ...  0.000821
629973     None  ...  0.215539
629974     None  ...  0.043184
629975     None  ...  0.358674
629976     None  ...  0.533665
629977     None  ...  0.035854
629978     None  ...  0.054233
629979     None  ...  0.737469
629980     None  ...  0.101494
629981     None  ...  0.035499

根据 geopandas 的文档，.area属性返回包含以CRS为单位表示的GeoSeries中每个几何图形的面积的系列".我很困惑这意味着什么，以及我如何使用这些信息来简单地为我的 shapefile 的几何图形(例如米^ 2)获取一个定义的区域.谢谢！

According to geopandas' docs, the .area attribute "Returns a Series containing the area of each geometry in the GeoSeries expressed in the units of the CRS." I'm very confused as to what this means, and how I can use this information to simply get a defined area for the geometries of my shapefile (e.g. meters^2). Thank you!

推荐答案

geopandas 计算面积最重要的部分是您必须使用对应于 equal-area 投影的 CRS.在这种情况下，简单的圆柱等积投影 (epsg=6933) 很好用.

The most important part of area computation by geopandas is that you must use the CRS that corresponds to an equal-area projection. In this case, the simple cylindrical equal-area projection (epsg=6933) is good to use.

数据文件可以从:- data_source

相关代码应该变成:

water = gp.read_file("/Users/user/Downloads/tlgdb_2020_a_us_areawater.gdb")

# check the CRS
water.crs
# you should find that it is already `epsg=4269`

# select some rows of data
lakeSup = water.loc[water['FULLNAME'].str.contains('Lk Superior', na=False)]

# lakeSup = lakeSup.to_crs(epsg=4269) # already is

# convert CRS to equal-area projection
# the length unit is now `meter`
eqArea_lakeSup = lakeSup.to_crs(epsg=6933)

# compute areas in sq meters
areas = eqArea_lakeSup.area

# set the area units to sq Km.
# and add it as a new column to geodataframe
eqArea_lakeSup["area_sqKm"] = areas.values/10e6

# print some result
print(eqArea_lakeSup[["FULLNAME","area_sqKm"]].head(10))

输出:

           FULLNAME   area_sqKm
233938  Lk Superior    0.695790
629973  Lk Superior  181.784389
629974  Lk Superior   36.563379
629975  Lk Superior  303.028792
629976  Lk Superior  446.529784
629977  Lk Superior   30.418959
629978  Lk Superior   45.785750
629979  Lk Superior  621.004141
629980  Lk Superior   86.142490
629981  Lk Superior   30.186412

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