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Tools for working with shapefiles, topographies, and polygons in xarray

Project description

xshape

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Tools for working with shapefiles, topographies, and polygons in xarray

Features

  • Read a shapefile and obtain an xarray DataArray of field records

  • Draw shapefile boundaries on gridded data

  • Plot xarray DataArray data indexed by shapefile records as a choropleth

Usage

Getting records for fields in a shapefile

In [1]: import xshape

In [2]: fields, polygons = xshape.parse_shapefile(
   ...:     'tests/data/shapefiles/CA_counties/CA_counties',
   ...:     encoding='latin1')

In [3]: fields
Out[3]:
<xarray.Dataset>
Dimensions:   (shape: 58)
Coordinates:
  * shape     (shape) int64 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 ...
Data variables:
    STATEFP   (shape) <U22 '06' '06' '06' '06' '06' '06' '06' '06' '06' '06' ...
    COUNTYFP  (shape) <U22 '107' '009' '047' '079' '097' '041' '023' '051' ...
    COUNTYNS  (shape) <U22 '00277318' '01675885' '00277288' '00277304' ...
    GEOID     (shape) <U22 '06107' '06009' '06047' '06079' '06097' '06041' ...
    NAME      (shape) <U22 'Tulare' 'Calaveras' 'Merced' 'San Luis Obispo' ...
    NAMELSAD  (shape) <U22 'Tulare County' 'Calaveras County' ...
    LSAD      (shape) <U22 '06' '06' '06' '06' '06' '06' '06' '06' '06' '06' ...
    CLASSFP   (shape) <U22 'H1' 'H1' 'H1' 'H1' 'H1' 'H1' 'H1' 'H1' 'H1' 'H1' ...
    MTFCC     (shape) <U22 'G4020' 'G4020' 'G4020' 'G4020' 'G4020' 'G4020' ...
    CSAFP     (shape) <U22 '' '' '' '' '488' '488' '' '' '' '' '488' '472' ...
    CBSAFP    (shape) <U22 '47300' '' '32900' '42020' '42220' '41860' ...
    METDIVFP  (shape) <U22 '' '' '' '' '' '41884' '' '' '' '' '36084' '' '' ...
    FUNCSTAT  (shape) <U22 'A' 'A' 'A' 'A' 'A' 'A' 'A' 'A' 'A' 'A' 'A' 'A' ...
    ALAND     (shape) <U22 '12494707314' '2641820029' '5011554680' ...
    AWATER    (shape) <U22 '37391604' '43810423' '112760479' '820974619' ...
    INTPTLAT  (shape) <U22 '+36.2288317' '+38.1846184' '+37.1948063' ...
    INTPTLON  (shape) <U22 '-118.7810618' '-120.5593996' '-120.7228019' ...

Drawing shape boundaries on gridded data

In [4]: import xarray as xr, numpy as np, xshape

# generate sample data
In [5]: da = xr.DataArray(
   ...:    np.cos((
   ...:         np.arange(41*45).reshape((41, 45)) * np.arange(41*45).reshape((45, 41)
   ...:         ).T)/4e5),
   ...:    dims=('lat', 'lon'),
   ...:    coords={
   ...:        'lon': np.linspace(-125, -114, 45),
   ...:        'lat': np.linspace(32, 42, 41)})
   ...:

In [6]: da.xshape.overlay(
   ...:     'tests/data/shapefiles/CA_counties/CA_counties',
   ...:     encoding='latin1',
   ...:     cmap='YlGnBu');
   ...:
<figure> docs/images/california_map.png </figure>

Plotting regional data in a choropleth

Using the xarray extension, we can plot DataArray data directly:

In [7]: import xshape, xarray as xr, pandas as pd

In [8]: df = pd.read_csv('tests/data/datasets/co-est2016.csv', encoding='latin1')
   ...: ca = df[(df['STATE'] == 6) & (df['COUNTY'] > 0)].copy()
   ...: ca['fips'] = df['STATE'] * 1000 + df['COUNTY']
   ...: da = ca.set_index(['fips'])['POPESTIMATE2016'].to_xarray()
   ...: da.coords['GEOID'] = ('fips', ), list(map('{:05}'.format, da.fips.values))
   ...: da = da.swap_dims({'fips': 'GEOID'})

In [9]: da.xshape.plot(
   ...:     'tests/data/shapefiles/CA_counties/CA_counties',
   ...:     encoding='latin1',
   ...:     cmap='YlGnBu');
   ...:
<figure> docs/images/california_map_pop.png </figure>

We can also combine the information from the fields with the data contained in the DataArray:

In [10]: land_area = (
   ....:     fields
   ....:     .set_coords('GEOID')
   ....:     .swap_dims({'shape': 'GEOID'})
   ....:     .ALAND.astype(float))

In [11]: np.log(da / land_area).xshape.plot(
   ....:     'tests/data/shapefiles/CA_counties/CA_counties',
   ....:     encoding='latin1',
   ....:     cmap='YlGnBu');
   ....:
<figure> docs/images/california_map_pop_per_m2.png </figure>

TODO

  • Use shapefiles to reshape gridded/pixel data

History

0.1.0 (2018-01-13)

  • First release on PyPI.

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