diff --git a/01-spatial-data.qmd b/01-spatial-data.qmd index 3827881f..cc3d5e17 100644 --- a/01-spatial-data.qmd +++ b/01-spatial-data.qmd @@ -615,15 +615,15 @@ multipolygon.area ``` ```{python} -gdf.area +gpd.GeoSeries([point, linestring, polygon, multipolygon]).area ``` Like all numeric calculations in **geopandas**, the results assume a planar CRS and are returned in its native units. -This means that length and area measurements for geometries in WGS84 (`crs=4326`) are returned in decimal degrees and essentially meaningless, thus the warning in the above command. +This means that length and area measurements for geometries in WGS84 (`crs=4326`) are returned in decimal degrees and essentially meaningless (to see the warning, try running `gdf.area`). -To obtain true length and area measurements, the geometries first need to be transformed to a projected CRS (see @sec-reprojecting-vector-geometries) applicable to the area of interest. +To obtain meaningful length and area measurements for data in a geographic CRS, the geometries first need to be transformed to a projected CRS (see @sec-reprojecting-vector-geometries) applicable to the area of interest. For example, the area of Slovenia can be calculated in the UTM zone 33N CRS (`crs=32633`). -The result is in $m^2$, the units of the CRS of this dataset. +The result is in $m^2$, the units of the CRS of this dataset. ```{python} gdf[gdf['name_long'] == 'Slovenia'].to_crs(32633).area