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I'm trying to start plotting maps in python with matplotlib's basemap, but every shapefile I've tried to far seems to have coordinates in metres instead of lat/lon, so I get the following error from readshapefile:

ValueError: shapefile must have lat/lon vertices - it looks like this one has vertices in map projection coordinates.

Here's output from fiona about the shapefile I'm using:

shape = fiona.open('./data/ESRI/London_Ward.shp') bounds = shape.bounds print(shape.crs)

: {'proj': 'tmerc', 'lat_0': 49, 'lon_0': -2, 'k': 0.999601272, 'x_0': 400000, 'y_0': -100000, 'datum': 'OSGB36', 'units': 'm', 'no_defs': True}

print(bounds)
: (503568.2, 155850.8, 561957.5, 200933.9)

ogr2ogr is the only conversion tool I've managed to install so far, is it possible to use it to make the necessary conversion?

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Yes, it is. Use it like this from the command line (might be necessary to cd into the folder where ogr2ogr has been installed to):

ogr2ogr -t_srs EPSG:4326 -f "ESRI Shapefile" transformed.shp London_Ward.shp

If you want to run it from Python, you can use subprocess to set up the command and run it from the script, e.g. like this:

import subprocess as sub

input = r'./data/ESRI/London_Ward.shp'
output = r'./data/ESRI/London_Ward_WGS84.shp'
cmd = 'ogr2ogr -t_srs EPSG:4326 -f "ESRI Shapefile" {0} {1}'.format(output, input)
p = sub.Popen(cmd, stdout=sub.PIPE, stderr=sub.PIPE)
stdout, stderr = p.communicate()
if p.exitcode != 0:
    print stdout
    print stderr

Alternatively, pass all parts of the command as a list like this:

p = sub.Popen([ogr2ogr -t_srs EPSG:4326 -f "ESRI Shapefile", output, input], stdout=sub.PIPE, stderr=sub.PIPE)

In case you really want to stay within Python and don't use the command line, use the accepted answer from Python - OGR: Transform coordinates from meter to decimal degrees

Also have a look at the Documentation

  • Thanks for the answer. I think it was mainly the command-line options for ogr2ogr I needed help with. Is there any reason you picked subprocess over os.system for running it in python? – thosphor Mar 19 '18 at 9:14
  • Not really... I was just trusting the answer from Difference between subprocess.Popen and os.system – s6hebern Mar 19 '18 at 12:37

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