How to create a feature collection after importing different shapefiles from assets in Google Earth Engine?

Question

I am importing 2 different shapefiles from assets to plot the time series chart of MODIS

but I am unable to make the feature collection out of these shapefiles

how to do that?

var Haryana_state = ee.FeatureCollection('users/abhilashaanu92/HaryanaBoundary');

Map.addLayer(Haryana_state);

var Punjab_state = ee.FeatureCollection('users/abhilashaanu92/punjab_state_boundary');

Map.addLayer(Punjab_state);

// Combine features into a feature collection.
var both_states = ee.FeatureCollection([Haryana_state, Punjab_state]).flatten();

Map.addLayer(both_states);

// Load MODIS vegetation indices data and subset annual images.


var vegIndices = ee.ImageCollection('MODIS/006/MOD13A1')
                     .filter(ee.Filter.date('2019-01-01', '2020-01-01'))
                     .select(['NDVI', 'EVI']);

// Define the chart and print it to the console.
var chart =
    ui.Chart.image
        .seriesByRegion({
          imageCollection: vegIndices,
          band: 'NDVI',
          regions: both_states,
          reducer: ee.Reducer.mean(),
          scale: 500,
          seriesProperty: 'label',
          xProperty: 'system:time_start'
        })
        .setOptions({
          title: 'Average NDVI Value by Date',
          hAxis: {title: 'Date', titleTextStyle: {italic: false, bold: true}},
          vAxis: {
            title: 'NDVI (x1e4)',
            titleTextStyle: {italic: false, bold: true}
          },
          lineWidth: 5,
          colors: ['f0af07', '0f8755', '76b349'],
        });
print(chart);

if I put the name of a single shapefile variable in the regions then it is working but when I combine the 2 shapefiles into a feature collection then it is showing the error.

How to rectify this?

I want output something like this. (the time series of both the states on the same chart).

Chart Source URL

Answer 1

Two things need to be done here. First, add .flatten() after combining the two FeatureCollections.

This way, you make a collection of features (FeatureCollection), which is desired. Otherwise, you end up with a collection of FeatureCollections, which prompts the error.

Second, the seriesProperty needs to match the label of your FeatureCollection. In this case, 'STATE_NAME'. You can check this by adding print(both_states) to check how your new FeatureCollection looks like. I've updated the code.

var Haryana_state = ee.FeatureCollection('users/abhilashaanu92/HaryanaBoundary');

Map.addLayer(Haryana_state);

var Punjab_state = ee.FeatureCollection('users/abhilashaanu92/punjab_state_boundary');

Map.addLayer(Punjab_state);

// Combine features into a feature collection.
var both_states = ee.FeatureCollection([Haryana_state, Punjab_state]).flatten();
print('Check the properties; this will tell you what seriesProperty to use', both_states)

Map.addLayer(both_states);

// Load MODIS vegetation indices data and subset annual images.


var vegIndices = ee.ImageCollection('MODIS/006/MOD13A1')
                     .filter(ee.Filter.date('2019-01-01', '2020-01-01'))
                     .select(['NDVI', 'EVI']);

// Define the chart and print it to the console.
var chart =
    ui.Chart.image
        .seriesByRegion({
          imageCollection: vegIndices,
          band: 'NDVI',
          regions: both_states,
          reducer: ee.Reducer.mean(),
          scale: 500,
          seriesProperty: 'STATE_NAME',
          xProperty: 'system:time_start'
        })
        .setOptions({
          title: 'Average NDVI Value by Date',
          hAxis: {title: 'Date', titleTextStyle: {italic: false, bold: true}},
          vAxis: {
            title: 'NDVI (x1e4)',
            titleTextStyle: {italic: false, bold: true}
          },
          lineWidth: 5,
          colors: ['f0af07', '0f8755', '76b349'],
        });
print(chart);