This GeoDataFrame has spatial data which is projected onto a specific coordinate reference system (CRS) which is not lat/lon. Latitude and Longitude coordinates need a specific definition of the shape of the earth and reference zero-points - one which is most commonly accepted as the standard is World Geodetic System 1984 (aka WGS84 aka EPSG:4326). Many times, when you load a shapefile, the data will be encoded as lat/lon using WGS84. But not always.
The .crs attribute of a GeoDataFrame or GeoSeries gives more information about the specific reference system used in encoding the data. In the case of this example:
In [3]: nybb_path = geopandas.datasets.get_path('nybb')
...: boros = geopandas.read_file(nybb_path)
...: boros.set_index('BoroCode', inplace=True)
...: boros.sort_index(inplace=True)
...:
In [4]: boros.crs
Out[4]:
<Derived Projected CRS: EPSG:2263>
Name: NAD83 / New York Long Island (ftUS)
Axis Info [cartesian]:
- X[east]: Easting (US survey foot)
- Y[north]: Northing (US survey foot)
Area of Use:
- name: United States (USA) - New York - counties of Bronx; Kings; Nassau; New York; Queens; Richmond; Suffolk.
- bounds: (-74.26, 40.47, -71.8, 41.3)
Coordinate Operation:
- name: SPCS83 New York Long Island zone (US Survey feet)
- method: Lambert Conic Conformal (2SP)
Datum: North American Datum 1983
- Ellipsoid: GRS 1980
- Prime Meridian: Greenwich
You can see that the coordinates in this dataset are in units of US survey feet referenced to the North American Datum 1983 (NAD83) (hence the large values), and are projected using a Lambert Conic Conformal (2SP) projection. This projection has advantages for mapping because, unlike an equi-rectangular projection, e.g. simply mapping lat/lon to pixels, a conformal projection will preserve angles (so e.g. street corners will look like right angles regardless of latitude).
You can change the projection using geopandas.GeoDataFrame.to_crs. GeoPandas uses pyproj to manage projections - the proj syntax for WGS84 is "epsg:4326":
In [5]: boros_latlon = boros.to_crs('epsg:4326')
In [6]: boros_latlon.crs
Out[6]:
<Geographic 2D CRS: EPSG:4326>
Name: WGS 84
Axis Info [ellipsoidal]:
- Lat[north]: Geodetic latitude (degree)
- Lon[east]: Geodetic longitude (degree)
Area of Use:
- name: World.
- bounds: (-180.0, -90.0, 180.0, 90.0)
Datum: World Geodetic System 1984 ensemble
- Ellipsoid: WGS 84
- Prime Meridian: Greenwich
Now, the shapes are expressed as lat/lon
In [7]: boros_latlon
Out[7]:
BoroName Shape_Leng Shape_Area \
BoroCode
1 Manhattan 359299.096471 6.364715e+08
2 Bronx 464392.991824 1.186925e+09
3 Brooklyn 741080.523166 1.937479e+09
4 Queens 896344.047763 3.045213e+09
5 Staten Island 330470.010332 1.623820e+09
geometry
BoroCode
1 MULTIPOLYGON (((-74.01093 40.68449, -74.01193 ...
2 MULTIPOLYGON (((-73.89681 40.79581, -73.89694 ...
3 MULTIPOLYGON (((-73.86706 40.58209, -73.86769 ...
4 MULTIPOLYGON (((-73.83668 40.59495, -73.83678 ...
5 MULTIPOLYGON (((-74.05051 40.56642, -74.05047 ...
See the geopandas guide to projections and coordinate reference systems for more information.
