[GIS] Updating GeoJSON properties

geojsonjavascriptjsonleaflet

Below is my demand.js file containing my geojson data:

var campus = {
    "type":"FeatureCollection",
    "features": [
        {
            "type": "Feature",     
            "id":"03",
            "properties": {
                "name": "ANG MO KIO",        
                "demand":"30"
            },
            "geometry": {
                "type": "MultiPolygon",
                "coordinates": [[[
                [103.866,1.37152],[103.862,1.36902],[103.861,1.36761],
                [103.858,1.36139],[103.858,1.36041],[103.857,1.35777],
                [103.856,1.35518],[103.856,1.35398],[103.856,1.35231],
                [103.855,1.35202],[103.854,1.3542],[103.852,1.35624],
                [103.849,1.35865],[103.845,1.3623],[103.844,1.36289],
                [103.842,1.36318],[103.84,1.36335],[103.837,1.36402],
                [103.835,1.36497],[103.831,1.36737],[103.831,1.36843],
                [103.831,1.36926],[103.832,1.36942],[103.832,1.37001],
                [103.832,1.37062],[103.833,1.37112],[103.833,1.3716],
                [103.833,1.3723],[103.833,1.37436],[103.834,1.3759],
                [103.834,1.37613],[103.835,1.37681],[103.835,1.37684],
                [103.836,1.37798],[103.834,1.381],[103.835,1.38121],
                [103.835,1.3814],[103.835,1.38167],[103.836,1.38199],
                [103.837,1.38406],[103.839,1.38606],[103.843,1.38912],
                [103.845,1.39041],[103.846,1.39135],[103.848,1.39194],
                [103.849,1.3922],[103.85,1.39244],[103.85,1.38615],
                [103.85,1.38403],[103.849,1.38206],[103.848,1.38064],
                [103.848,1.37963],[103.848,1.379],[103.848,1.37854],
                [103.849,1.37788],[103.852,1.37726],[103.855,1.37695],
                [103.857,1.37718],[103.861,1.37839],[103.863,1.37881],
                [103.866,1.37889],[103.867,1.3787],[103.868,1.37834],
                [103.872,1.37663],[103.869,1.37614],[103.869,1.37564],
                [103.867,1.37429],[103.867,1.37276],[103.866,1.37152]
                ]]]
            } 
        }
    ]
};

function setDemand(id, newdemand) {   
    for (var i=0; i<campus.length;i++) {
        if (campus[i].features.id > id) {
            campus[i].features.properties.demand = newdemand;
            return;
        } else {
            campus[i].features.properties.demand = newdemand+100;
        }     
    }    
}

The setDemand function is called when the select button is triggered:

<select onchange="setDemand(10,1000)">

But it does not work – the properties do not change. I am new to geoJSON/JSON.

Best Answer

Note that campus is not an array, so you can not do

campus[i]

Instead, campus is a plain javascript object with a features property which is an array, so you can do

campus.features[i]

In order to change a property of the i-th feature in a GeoJSON FeatureCollection, just

campus.features[i].properties.demand = newValue;

Your original question had a syntax error in the GeoJSON (an additional set of brackets). If you're new to GeoJSON and you are writing the GeoJSON structures by yourself, please use a tool like http://geojsonlint.com/ to make sure that the structures are valid.

Related Question