For an application I want to determine under which constituency a given coordinate falls. After looking at the various options, I decided upon shapely and fiona as the easiest way to implement this. Here is what I wrote for testing if a given coordinate is within a given constituency.
import fiona
import shapely.geometry
fc = fiona.open("shapefile.shp")
shapefile_record = fc.next()
shape = shapely.geometry.asShape(shapefile_record['geometry'])
def is_constituency(lat,lng):
point = shapely.geometry.Point(lat,lng)
print shape.contains(point)
This yields false for all tests, even when I am sure the coordinate falls within said constituency.
To give an example, the first record
>>> shapefile_record['properties']
OrderedDict([(u'DIST_NAME', u'Uttarkashi'), (u'Assem_No', 2), (u'AREA', 0.003), (u'PERIMETER', 0.381), (u'INDIAASSEM', 2802.0), (u'INDIAASS', 0.0), (u'NO', 0.0), (u'ST_CODE', u'S28'), (u'AC_NAME', u'GANGOTRI'), (u'AC_TYPE', u'GEN'), (u'PC_NO', 0.0), (u'AC_NO', 2.0), (u'AC_HNAME', u'\x90\xd6\xd3\x90\xd6\xd6\xea\xa1\xd6\xdf'), (u'PARTY', u'INC'), (u'CODE_NO', u'S282'), (u'Longitude', 78.8900584624), (u'Latitude', 30.9787742252), (u'State', u'Uttaranchal'), (u'PC_NAME', u'Tehri Garhwal'), (u'PC_TYPE', u'GEN'), (u'PC_CODE', u'S2801'), (u'PC_NO_1', 1)])
Choosing the point right at the center of the constituency as described in the shapefile gives me false
>>>is_constituency(30.9787, 78.8900)
False
To make it even clearer that this is wrong, consider this:
>>> shape.contains(shapely.geometry.Point(shapefile_record['properties']['Latitude'],shapefile_record['properties']['Longitude']))
False
This means that latitude and longitude that define a polygon in its shapefile are not in the polygon?
What am I doing wrong? The whole geometry of this particular record is here:
>>> shapefile_record['geometry']
{'type': 'Polygon', 'coordinates': [[(78.38236181915738, 31.26909614048731), (78.37916181915745, 31.268796140487385), (78.3822618191574, 31.267896140487327), (78.3863618191574, 31.25889614048731), (78.38236181915738, 31.26909614048731), (78.39066181915734, 31.27209614048735), (78.39166181915749, 31.26569614048737), (78.39476181915734, 31.261196140487364), (78.40206181915738, 31.253896140487317), (78.40136181915733, 31.247396140487414), (78.40616181915749, 31.242696140487347), (78.40616181915749, 31.23999614048722), (78.42386181915737, 31.242196140487348), (78.42906181915743, 31.251396140487262), (78.43636181915747, 31.24869614048731), (78.43946181915743, 31.241396140487275), (78.45286181915736, 31.236896140487264), (78.46626181915747, 31.219596140487393), (78.47446181915734, 31.213196140487415), (78.47546181915749, 31.203196140487254), (78.47896181915735, 31.201496140487286), (78.47846181915736, 31.194996140487323), (78.47896181915735, 31.19249614048727), (78.48206181915737, 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31.079496140487276), (77.86486181915738, 31.08949614048727), (77.86586181915737, 31.094896140487307), (77.87106181915738, 31.100496140487337), (77.88666181915741, 31.107896140487316), (77.89296181915745, 31.10979614048731), (77.89296181915745, 31.117096140487327), (77.89396181915743, 31.122496140487275), (77.9032618191574, 31.133596140487274), (77.90116181915737, 31.139896140487284), (77.90636181915737, 31.142696140487285), (77.91476181915738, 31.143696140487275), (77.92206181915738, 31.140996140487285), (77.92836181915737, 31.141996140487276), (77.94716181915737, 31.153096140487285), (77.95136181915737, 31.153196140487275), (77.95336181915737, 31.156796140487273), (77.95856181915737, 31.162396140487285), (77.96796181915737, 31.164296140487277), (77.98266181915737, 31.15079614048728), (77.99936181915737, 31.15369614048728), (78.00566181915737, 31.152796140487283), (78.01926181915736, 31.143796140487275), (78.02756181915737, 31.141196140487278), (78.03066181915744, 31.1453961404873), (78.03266181915738, 31.137896140487282), (78.03166181915748, 31.14599614048723), (78.03166181915748, 31.151296140487382), (78.03066181915744, 31.1453961404873), (78.02866181915738, 31.152096140487295), (78.02856181915746, 31.15849614048733), (78.04006181915736, 31.166796140487293), (78.04316181915738, 31.17229614048728), (78.05156181915748, 31.174196140487254), (78.0661618191574, 31.17979614048733), (78.08706181915738, 31.17999614048739), (78.09226181915739, 31.178196140487334), (78.09856181915728, 31.178296140487422), (78.10586181915733, 31.181096140487284), (78.11416181915752, 31.18849614048742), (78.12046181915741, 31.191296140487285), (78.12256181915745, 31.1939961404874), (78.12566181915747, 31.194996140487323), (78.13196181915737, 31.20229614048736), (78.14656181915745, 31.20519614048737), (78.14866181915744, 31.21159614048736), (78.15756181915737, 31.2143961404874), (78.16006181915748, 31.21989614048738), (78.16736181915735, 31.21909614048741), (78.17266181915744, 31.2208961404873), (78.17786181915744, 31.220096140487392), (78.18206181915735, 31.220996140487273), (78.18726181915736, 31.219296140487305), (78.19876181915743, 31.212096140487347), (78.20396181915748, 31.21119614048729), (78.21126181915736, 31.214896140487387), (78.21436181915749, 31.223096140487257), (78.2185618191574, 31.226796140487355), (78.2237618191574, 31.227796140487325), (78.2289618191574, 31.228796140487248), (78.24256181915734, 31.2251961404873), (78.24886181915741, 31.229796140487394), (78.24886181915741, 31.234396140487327), (78.25406181915747, 31.23349614048732), (78.25926181915747, 31.237196140487356), (78.26026181915745, 31.24089614048728), (78.26346181915733, 31.243696140487316), (78.26556181915737, 31.24729614048727), (78.27286181915741, 31.255596140487285), (78.28016181915746, 31.262096140487422), (78.28846181915748, 31.25759614048741), (78.29786181915733, 31.25489614048729), (78.30416181915746, 31.25679614048727), (78.30626181915744, 31.264996140487373), (78.30626181915744, 31.275096140487285), (78.30946181915738, 31.277896140487314), (78.31566181915736, 31.276996140487256), (78.32606181915742, 31.276196140487347), (78.33656181915751, 31.278996140487383), (78.34486181915736, 31.277296140487415), (78.3573618191574, 31.28099614048728), (78.36576181915734, 31.28199614048725), (78.37826181915739, 31.279396140487226), (78.38236181915738, 31.26909614048731)]]}
The data I am using can be found here.
Answer
If we examine your polygon:
polygon = shapefile_record['geometry']
print polygon.bounds
(77.84476181915733, 30.711096140487314, 78.59476181915738, 31.28199614048725)
From Shapely manual, object.bounds:
Returns a (minx, miny, maxx, maxy) tuple (float values) that bounds the object.
Here minx = 77.84476181915733, miny = 30.711096140487314
= here, min longitude = 77.844... and min latitude = 30.711...
Setting your point as Point(30.9787, 78.8900) or Point(latitude, longitude), you reverse the coordinates:
your_point = Point(30.9787, 78.8900) # = Point(y, x)
xy_point = Point(78.8900,30.9787) # = Point(x,y)
polygon.contains(xy_point)
False
Which is correct:
So, the script with your example:
from shapely.geometry import Point, shape
point = Point(78.8900,30.9787)
fc = fiona.open("AC_All_Final.shp")
print fc.schema
{'geometry': 'Polygon', 'properties': OrderedDict([(u'DIST_NAME', 'str:254'), (u'Assem_No', 'int:4'), (u'AREA', 'float:18.3'), (u'PERIMETER', 'float:18.3'), (u'INDIAASSEM', 'float:11'), (u'INDIAASS', 'float:11'), (u'NO', 'float:11'), (u'ST_CODE', 'str:254'), (u'AC_NAME', 'str:254'), (u'AC_TYPE', 'str:254'), (u'PC_NO', 'float:11'), (u'AC_NO', 'float:19.11'), (u'AC_HNAME', 'str:254'), (u'PARTY', 'str:254'), (u'CODE_NO', 'str:254'), (u'Longitude', 'float:19.17'), (u'Latitude', 'float:19.17'), (u'State', 'str:50'), (u'PC_NAME', 'str:25'), (u'PC_TYPE', 'str:3'), (u'PC_CODE', 'str:10'), (u'PC_NO_1', 'int:4')])}
from feature in fc:
if shape(feature['geometry']).contains(point):
print feature['properties']['DIST_NAME'], feature['properties']['Longitude'], feature['properties']['Latitude']
Uttarkashi 78.8900584624 30.9787742252
Result:
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