9

I have a Geojson file with some adjacent polygons and I want to merge them into one. I know it's a recurrent question but I can't find information for polygons with latitude and longitude coordinates like in this geojson :

{
"type": "FeatureCollection",
"features": [{
    "type": "Feature",
    "id": "16966",
    "properties": {
        "Name": "BEYNES"
    },
    "geometry": {
        "type": "Polygon",
        "coordinates": [
            [
                [1.874862143378, 48.834371283832],
                [1.8656030688715, 48.831612507285],
                [1.8515105581603, 48.834338209867],
                [1.8466221791684, 48.828669687135],
                [1.8415374906793, 48.828818416443],
                [1.8392188748285, 48.830163082204],
                [1.8419058888315, 48.843509743804],
                [1.8472716401406, 48.849200964455],
                [1.8375210341485, 48.856814659389],
                [1.8383984699903, 48.87125874614],
                [1.8572939822902, 48.871944300476],
                [1.874663272221, 48.877028568925],
                [1.8831026195664, 48.874535338148],
                [1.9127169447188, 48.860849357594],
                [1.9030441003473, 48.846352529476],
                [1.8932786620468, 48.847377864779],
                [1.8885787644301, 48.846659731042],
                [1.8820915893247, 48.834609966105],
                [1.874862143378, 48.834371283832]
            ]
        ]
    }
}, {
    "type": "Feature",
    "id": "19484",
    "properties": {
        "Name": "VILLIERS-LE-MAHIEU"
    },
    "geometry": {
        "type": "Polygon",
        "coordinates": [
            [
                [1.7780400297013, 48.832305931728],
                [1.7734339848429, 48.83177307884],
                [1.7611156919393, 48.841036344684],
                [1.7664174460888, 48.850202460021],
                [1.7590182348483, 48.858733519882],
                [1.7586155859222, 48.868766940337],
                [1.7751309254077, 48.872615718624],
                [1.7866538204874, 48.862012015338],
                [1.7869427495986, 48.855458134055],
                [1.7916969548512, 48.854399942691],
                [1.7780400297013, 48.832305931728]
            ]
        ]
    }
}, {
    "type": "Feature",
    "id": "19635",
    "properties": {
        "Name": "THOIRY"
    },
    "geometry": {
        "type": "Polygon",
        "coordinates": [
            [
                [1.7916969548512, 48.854399942691],
                [1.7869427495986, 48.855458134055],
                [1.7866538204874, 48.862012015338],
                [1.7751309254077, 48.872615718624],
                [1.7890825137274, 48.88596098882],
                [1.809924587051, 48.885828200975],
                [1.8232153433812, 48.876452907166],
                [1.8120930366694, 48.869687419516],
                [1.8059996841005, 48.860128943481],
                [1.7916969548512, 48.854399942691]
            ]
        ]
    }
}, {
    "type": "Feature",
    "id": "22025",
    "properties": {
        "Name": "SAINT-GERMAIN-DE-LA-GRANGE"
    },
    "geometry": {
        "type": "Polygon",
        "coordinates": [
            [
                [1.9130661363292, 48.819937951319],
                [1.9012689316149, 48.821961792363],
                [1.8902265103296, 48.83135783825],
                [1.8813533302838, 48.831553995346],
                [1.8820915893247, 48.834609966105],
                [1.8885787644301, 48.846659731042],
                [1.8932786620468, 48.847377864779],
                [1.918172631346, 48.835751243515],
                [1.9217370910726, 48.82612360123],
                [1.9178385858043, 48.820341013587],
                [1.9130661363292, 48.819937951319]
            ]
        ]
    }
}, {
    "type": "Feature",
    "id": "22141",
    "properties": {
        "Name": "MARCQ"
    },
    "geometry": {
        "type": "Polygon",
        "coordinates": [
            [
                [1.8248465610939, 48.850691703059],
                [1.8126901224641, 48.853063092402],
                [1.8059996841005, 48.860128943481],
                [1.8120930366694, 48.869687419516],
                [1.8232153433812, 48.876452907166],
                [1.832123740674, 48.878689723796],
                [1.8383984699903, 48.87125874614],
                [1.8375210341485, 48.856814659389],
                [1.8246539514431, 48.853792824064],
                [1.8248465610939, 48.850691703059]
            ]
        ]
    }
}, {
    "type": "Feature",
    "id": "23142",
    "properties": {
        "Name": "PLAISIR"
    },
    "geometry": {
        "type": "Polygon",
        "coordinates": [
            [
                [1.9859353011511, 48.799648360798],
                [1.9700422200803, 48.799863243499],
                [1.9568703127355, 48.789270428369],
                [1.9412379043212, 48.791543482649],
                [1.9149109434793, 48.802631449948],
                [1.9130661363292, 48.819937951319],
                [1.9178385858043, 48.820341013587],
                [1.9217370910726, 48.82612360123],
                [1.9308900413011, 48.82617879826],
                [1.9432582596776, 48.836964867387],
                [1.9687926794162, 48.834831269347],
                [1.9700860589995, 48.83487839014],
                [1.9668984852354, 48.821791311587],
                [1.9864791162903, 48.799688951127],
                [1.9859353011511, 48.799648360798]
            ]
        ]
    }
}, {
    "type": "Feature",
    "id": "25041",
    "properties": {
        "Name": "NEAUPHLE-LE-CHATEAU"
    },
    "geometry": {
        "type": "Polygon",
        "coordinates": [
            [
                [1.9149109434793, 48.802631449948],
                [1.898492103809, 48.809622894015],
                [1.8936915762635, 48.808670122548],
                [1.8889579820032, 48.809057956502],
                [1.9012689316149, 48.821961792363],
                [1.9130661363292, 48.819937951319],
                [1.9149109434793, 48.802631449948]
            ]
        ]
    }
}, {
    "type": "Feature",
    "id": "25042",
    "properties": {
        "Name": "VICQ"
    },
    "geometry": {
        "type": "Polygon",
        "coordinates": [
            [
                [1.8479013041869, 48.812707864194],
                [1.8290034942099, 48.811265015475],
                [1.8111878056542, 48.814965840962],
                [1.8138162274863, 48.821557956532],
                [1.8061163949282, 48.830053068487],
                [1.8260692281346, 48.8296929387],
                [1.8327204785815, 48.833814514469],
                [1.8392188748285, 48.830163082204],
                [1.8415374906793, 48.828818416443],
                [1.8479013041869, 48.812707864194]
            ]
        ]
    }
}, {
    "type": "Feature",
    "id": "28635",
    "properties": {
        "Name": "ANDELU"
    },
    "geometry": {
        "type": "Polygon",
        "coordinates": [
            [
                [1.8232153433812, 48.876452907166],
                [1.809924587051, 48.885828200975],
                [1.7890825137274, 48.88596098882],
                [1.7831043145867, 48.891413707227],
                [1.8056581682382, 48.898808951748],
                [1.8355241961203, 48.88517153445],
                [1.832123740674, 48.878689723796],
                [1.8232153433812, 48.876452907166]
            ]
        ]
    }
}, {
    "type": "Feature",
    "id": "29431",
    "properties": {
        "Name": "GOUPILLIERES"
    },
    "geometry": {
        "type": "Polygon",
        "coordinates": [
            [
                [1.7586155859222, 48.868766940337],
                [1.7399133540032, 48.871449653856],
                [1.7412768098614, 48.874270196957],
                [1.7500295563815, 48.875450216663],
                [1.7522176666426, 48.87802738985],
                [1.7483369243043, 48.879497893862],
                [1.7704322974105, 48.896069058229],
                [1.7831043145867, 48.891413707227],
                [1.7890825137274, 48.88596098882],
                [1.7751309254077, 48.872615718624],
                [1.7586155859222, 48.868766940337]
            ]
        ]
    }
}, {
    "type": "Feature",
    "id": "30394",
    "properties": {
        "Name": "SAULX-MARCHAIS"
    },
    "geometry": {
        "type": "Polygon",
        "coordinates": [
            [
                [1.8392188748285, 48.830163082204],
                [1.8327204785815, 48.833814514469],
                [1.8339180317868, 48.843621026126],
                [1.8248465610939, 48.850691703059],
                [1.8246539514431, 48.853792824064],
                [1.8375210341485, 48.856814659389],
                [1.8472716401406, 48.849200964455],
                [1.8419058888315, 48.843509743804],
                [1.8392188748285, 48.830163082204]
            ]
        ]
    }
}, {
    "type": "Feature",
    "id": "34743",
    "properties": {
        "Name": "OSMOY"
    },
    "geometry": {
        "type": "Polygon",
        "coordinates": [
            [
                [1.7164466657999, 48.854920532859],
                [1.7052218923542, 48.860142271734],
                [1.7018533752573, 48.865673293225],
                [1.7198777076843, 48.872271383422],
                [1.7292022608762, 48.871219483604],
                [1.7274882838909, 48.859337782823],
                [1.7164466657999, 48.854920532859]
            ]
        ]
    }
}, {
    "type": "Feature",
    "id": "35495",
    "properties": {
        "Name": "FLEXANVILLE"
    },
    "geometry": {
        "type": "Polygon",
        "coordinates": [
            [
                [1.7400314884878, 48.837820948808],
                [1.7329083268502, 48.84610157804],
                [1.7189195066054, 48.848587971564],
                [1.7164466657999, 48.854920532859],
                [1.7274882838909, 48.859337782823],
                [1.7292022608762, 48.871219483604],
                [1.7314395279166, 48.873968471423],
                [1.7399133540032, 48.871449653856],
                [1.7586155859222, 48.868766940337],
                [1.7590182348483, 48.858733519882],
                [1.7664174460888, 48.850202460021],
                [1.7611156919393, 48.841036344684],
                [1.7400314884878, 48.837820948808]
            ]
        ]
    }
}, {
    "type": "Feature",
    "id": "36858",
    "properties": {
        "Name": "THIVERVAL-GRIGNON"
    },
    "geometry": {
        "type": "Polygon",
        "coordinates": [
            [
                [1.9687926794162, 48.834831269347],
                [1.9432582596776, 48.836964867387],
                [1.9308900413011, 48.82617879826],
                [1.9217370910726, 48.82612360123],
                [1.918172631346, 48.835751243515],
                [1.8932786620468, 48.847377864779],
                [1.9030441003473, 48.846352529476],
                [1.9127169447188, 48.860849357594],
                [1.9217113433858, 48.85832247492],
                [1.9613817024309, 48.851891899558],
                [1.970646933861, 48.840972240396],
                [1.9687926794162, 48.834831269347]
            ]
        ]
    }
}, {
    "type": "Feature",
    "id": "37629",
    "properties": {
        "Name": "NEAUPHLE-LE-VIEUX"
    },
    "geometry": {
        "type": "Polygon",
        "coordinates": [
            [
                [1.8726237069958, 48.798651240921],
                [1.8711691241023, 48.799177186792],
                [1.8417552547252, 48.800622726785],
                [1.8479013041869, 48.812707864194],
                [1.8415374906793, 48.828818416443],
                [1.8466221791684, 48.828669687135],
                [1.8515105581603, 48.834338209867],
                [1.8656030688715, 48.831612507285],
                [1.874862143378, 48.834371283832],
                [1.8658960165459, 48.822530967257],
                [1.8689494730467, 48.8130077893],
                [1.8850727051194, 48.805432976807],
                [1.8858999508989, 48.804316374995],
                [1.8758215111851, 48.805049510395],
                [1.8726237069958, 48.798651240921]
            ]
        ]
    }
}, {
    "type": "Feature",
    "id": "38841",
    "properties": {
        "Name": "MONTAINVILLE"
    },
    "geometry": {
        "type": "Polygon",
        "coordinates": [
            [
                [1.8383984699903, 48.87125874614],
                [1.832123740674, 48.878689723796],
                [1.8355241961203, 48.88517153445],
                [1.8585137392849, 48.890942160516],
                [1.8687589726649, 48.885193372296],
                [1.874663272221, 48.877028568925],
                [1.8572939822902, 48.871944300476],
                [1.8383984699903, 48.87125874614]
            ]
        ]
    }
}, {
    "type": "Feature",
    "id": "43121",
    "properties": {
        "Name": "VILLIERS-SAINT-FREDERIC"
    },
    "geometry": {
        "type": "Polygon",
        "coordinates": [
            [
                [1.8850727051194, 48.805432976807],
                [1.8689494730467, 48.8130077893],
                [1.8658960165459, 48.822530967257],
                [1.874862143378, 48.834371283832],
                [1.8820915893247, 48.834609966105],
                [1.8813533302838, 48.831553995346],
                [1.8902265103296, 48.83135783825],
                [1.9012689316149, 48.821961792363],
                [1.8889579820032, 48.809057956502],
                [1.8936915762635, 48.808670122548],
                [1.8940011070565, 48.805632849681],
                [1.8850727051194, 48.805432976807]
            ]
        ]
    }
}]

}

raw polygons

Is there a way to build a master polygon with the external form of all polygons?

12

You can use Mapshaper for this, and then dissolve from the command line:

mapshaper --dissolve -i your_data.geojson
  • 2
    Great tool. If you get syntax errors, try it like mapshaper -i your_data.geojson --dissolve – Kyle Hotchkiss May 17 '16 at 23:54
4

It's easy to do with QGis.

  1. Open QGis
  2. Drag&Drop the geojson file to qgis
  3. use the "dissolve" tool in the vector menu (it's inside a submenu). use the "dissolve all" option from the dropdown
  4. this will create a shapefile (check the box to output to the map)
  5. which you can then again save as a geojson file by right-clicking it in the layer pane and choosing "save as" and then geojson as format

"Dissolve" is the name of the operation you want. This might alsio give you further hints for googling.

  • 1
    thanks til_b for your proposition, I use the jayarem one but yours look nice too but less scalable – henri_1310 Oct 14 '14 at 15:36
  • Yes it is less scalable. Didn't know about mapshaper before - so i learned new stuff also! – til_b Oct 14 '14 at 15:47
  • Thanks for pointing me to the dissolve tool. I followed your steps and almost got what I wanted, except for the error below. It outputed the layer I wanted, except feature 44 was cut out. Any suggestion on how to find out what exactly was invalid? The error message: Feature (44) has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the "Ignore invalid input features" option. – carpiediem May 25 '18 at 6:24
  • 1
    Got it. Toolbox > Vector Geometry > Fix geometries – carpiediem May 25 '18 at 6:30

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