Creating 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?

// 1st Shapefile
var Haryana_state = ee.FeatureCollection('users/abhilashaanu92/HaryanaBoundary');

Map.addLayer(Haryana_state);


// 2nd Shapefile
var Punjab_state = ee.FeatureCollection('users/abhilashaanu92/punjab_state_boundary');

Map.addLayer(Punjab_state);

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

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.

Error generating chart: Collection.geometry: Unable to use a collection in an algorithm that requires a feature or image. This may happen when trying to use a collection of collections where a collection of features is expected; use flatten, or map a function to convert inner collections to features. Use clipToCollection (instead of clip) to clip an image to a collection.

How to rectify this?

After adding .flatten() as in here

var both_states = ee.FeatureCollection([Haryana_state, Punjab_state]).flatten();

both the polygons merged into a single layer and the chart drawn was of the Punjab region only, as the values I cross-checked after exporting the CSV of Chart.

but I want a chart something like this, where the time-series is of both Haryana and Punjab on the same chart.

Answer 1

I know that you are implementing literally the code for ui.Chart.image.seriesByRegion from this link. For this reason you have two issues in your code. First one: you need to scale images for obtaining true values for NDVI. Second one: your feature collection doesn't have a 'label' property (each feature needs one with name of each state).

So, as I don't have a Haryana_state and a Punjab_state in my assets, I named two of my geometries in my assets with these names. I also added a 'label' property to each feature for testing my approach. My code looks as follows:

function prepImages (img){
  
  var time = img.get('system:time_start');
  
  return img.divide(10000)
    .set('system:time_start', time);
  
}

// 1st Shapefile
var Haryana_state = ee.FeatureCollection("users/joseguerreroa/indice_severidad/chapelco_32719");

Map.addLayer(Haryana_state);

// 2nd Shapefile
var Punjab_state = ee.FeatureCollection("users/joseguerreroa/indice_severidad/huiliches");

Map.addLayer(Punjab_state);

// Combine both shapefile features into a single feature collection.
var both_states = ee.FeatureCollection([ee.Feature(Haryana_state.geometry())
                                        .set('label', 'Haryana_state'), 
                                        ee.Feature(Punjab_state.geometry())
                                        .set('label', 'Punjab_state')]);

print(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'])
                     .map(prepImages);

// 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: 2,
          colors: ['f0af07', '0f8755', '76b349'],
        });
print(chart);

After running above code in GEE code editor, it was printed the chart as expected.