How to plot geo-data using matplotlib/python?

How to plot geo-data using matplotlib/python

• I am trying to plot a polygone on python, using different libararies, but no one of these worked with me. I tried https://github.com/wrobstory/vincent ,https://pypi.python.org/pypi/Shapely , .. and now matplotlib. I don't wanna use softwares like http://www.qgis.org/en/site/ I used this example: http://geographika.co.uk/visualising-geojson-in-15-minutes from matplotlib import pyplot from descartes import PolygonPatch import math import urllib2 import simplejson data = [] with open('file.json') as f: for line in f: data.append(json.loads(line)) def plotFeature(coordlist, myplot): #create a polygon geojson-like feature poly = {"type": "Polygon", "coordinates": coordlist} patch = PolygonPatch(poly, fc='#6699cc', ec='#6699cc', alpha=0.5, zorder=2) #plot it on the graph myplot.add_patch(patch) for coordlist in data['features'][0]['geometry']['coordinates']: plotFeature(coordlist, myplot) fig = pyplot.figure(1, figsize=(10, 4), dpi=180) ax = fig.add_subplot(121) ax.savefig('myplot.png') External file "file.json" var states = [{ "type": "Feature", "properties": {"party": "Republican"}, "geometry": { "type": "Polygon", "coordinates": [ [ [ -84.32281494140625, 34.9895035675793 ], [ -84.29122924804688, 35.21981940793435 ], [ -84.24041748046875, 35.25459097465022 ], [ -84.22531127929688, 35.266925688950074 ], [ -84.20745849609375, 35.26580442886754 ], [ -84.19921875, 35.24674063355999 ], [ -84.16213989257812, 35.24113278166642 ], [ -84.12368774414062, 35.24898366572645 ], [ -84.09072875976562, 35.24898366572645 ], [ -84.08798217773438, 35.264683153268116 ], [ -84.04266357421875, 35.27701633139884 ], [ -84.03030395507812, 35.291589484566124 ], [ -84.0234375, 35.306160014550784 ], [ -84.03305053710936, 35.32745068492882 ], [ -84.03579711914062, 35.34313496028189 ], [ -84.03579711914062, 35.348735749472546 ], [ -84.01657104492188, 35.35545618392078 ], [ -84.01107788085938, 35.37337460834958 ], [ -84.00970458984374, 35.39128905521763 ], [ -84.01931762695312, 35.41479572901859 ], [ -84.00283813476562, 35.429344044107154 ], [ -83.93692016601562, 35.47409160773029 ], [ -83.91220092773438, 35.47632833265728 ], [ -83.88885498046875, 35.504282143299655 ], [ -83.88473510742186, 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I need to plot these coordinates with a map on background. Any example, library, tutorial to recommend ?

• Answer:

  You cannot apply this particular example without understanding the JSON format: your external file "file.json" is not an .json file A correct format would be (without var states = [:) { "type": "Feature", "properties": {"party": "Republican"}, "geometry": { "type": "Polygon", "coordinates": [ [ [ -84.32281494140625, 34.9895035675793 .... } } To process this file, you can use the standard https://docs.python.org/2/library/json.html module or directly the https://pypi.python.org/pypi/geojson/1.0.6 module instead of the https://pypi.python.org/pypi/simplejson/ module, deprecated since Python 2.6 (for Python versions < 2.6) Read and parse the file: import json # or import geojson with open("file.json") as json_file: json_data = json.load(json_file) # or geojson.load(json_file) The result is a classic Python dictionary with the keys: print json_data.keys() [u'geometry', u'type', u'properties'] The geometry is : poly = json_data['geometry'] print poly {u'type': u'Polygon', u'coordinates': [[[-84.32281494140625, 34.989503567579298], [-84.291229248046875, 35.219819407934352], ..., [-75.690307617187486, 35.742053830680369]]]} This result is directly usable with https://pypi.python.org/pypi/descartes/1.0.1 and you don't need poly = {"type": "Polygon", "coordinates": coordlist} import matplotlib.pyplot as plt from descartes import PolygonPatch BLUE = '#6699cc' fig = plt.figure() ax = fig.gca() ax.add_patch(PolygonPatch(poly, fc=BLUE, ec=BLUE, alpha=0.5, zorder=2 )) ax.axis('scaled') plt.show() But you can also use the coordinates to plot the outer ring of the polygon coords = json_data['geometry']['coordinates'] print coords [[[-84.32281494140625, 34.989503567579298], [-84.291229248046875, 35.219819407934352],....[-75.690307617187486, 35.742053830680369]]] x = [i for i,j in coords[0]] y = [j for i,j in coords[0]] ax = fig.gca() ax.plot(x,y) ax.axis('scaled')