population dynamics

// define the countries of interest in this list
var countryList = ["Cambodia","Vietnam","Laos","Burma","Thailand"];
// import the country boundaries and filter for the countries of interest
var countries = ee.FeatureCollection('USDOS/LSIB_SIMPLE/2017').filter(ee.Filter.inList("country_na", countryList));

// import worldpop data
var wp = ee.ImageCollection("WorldPop/GP/100m/pop").filterBounds(countries);


// set the start and end dates
var start = ee.Date.fromYMD(2020,1,1);
var end = ee.Date.fromYMD(2020,12,31);

// filter for the period of interest
var wp2020 = ee.Image(wp.filterDate(start,end).mean());
// clip for the area of interest
wp2020 = wp2020.clip(countries);

// Define the chart and print it to the console.
var chart =
    ui.Chart.image.seriesByRegion
        ({
          imageCollection:wp,
          regions: aoi,
          reducer: ee.Reducer.sum(),
          scale: 100,
          xProperty: 'system:time_start'
        })
        .setSeriesNames(['population'])
        .setOptions({
          title: 'population dynamics',
          hAxis: {title: 'Date', titleTextStyle: {italic: false, bold: true}},
          vAxis: {
            title: 'total population',
            titleTextStyle: {italic: false, bold: true}
          },
          lineWidth: 5,
          colors: ['e37d05'],
          curveType: 'function'
        });
        
print(chart);