# calculating population dynamics

looking at time series

Step 1: import the administrative boundaries used for selecting the area of interest

```// define the countries of interest in this list
var countryList = ["Cambodia"];
// 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));
// add the layer to the map
```

Step 2: import the worldPop dataset and filter for area of interest

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

Step 3: filter for date and show the results of they year 2000

```// set the start and end dates
var start = ee.Date.fromYMD(2000,1,1);
var end = ee.Date.fromYMD(2000,12,31);

// filter for the period of interest
var wp2000 = ee.Image(wp.filterDate(start,end).mean());
// clip for the area of interest
wp2000 = wp2000.clip(countries);
```

step 4: do the same for the year 2020

```// 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);
```

step 5: copy the code below to calculate the total population

```var totalPopulation2000 = wp2000.reduceRegion({reducer:ee.Reducer.sum(),scale:100,maxPixels:1e13,geometry:countries});
print(totalPopulation2000);

var totalPopulation2020 = wp2020.reduceRegion({reducer:ee.Reducer.sum(),scale:100,maxPixels:1e13,geometry:countries});
print(totalPopulation2020);
```

step 6: use the code below to study the population dynamics from 2000 – 2020

```// Define the chart and print it to the console.
var chart =
ui.Chart.image.seriesByRegion
({
imageCollection:wp,
regions: countries,
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);
```

step 7: import the administrative layers

```// import administrative layers

// show layers on map
```

step 8: analyse the population per province

```// Define the chart and print it to the console.
var chart =
ui.Chart.image.byRegion
({
image:wp2020,
regions: provinces,
reducer: ee.Reducer.sum(),
scale: 100,
xProperty: 'NAME_1'

})
.setSeriesNames(['population'])
.setOptions({
title: 'Population per province',
hAxis: {title: 'Province', titleTextStyle: {italic: false, bold: true}},
vAxis: {
title: 'total population',
titleTextStyle: {italic: false, bold: true}
}
}).setChartType('ColumnChart');;

print(chart);
```

Questions:

1. how to calculate total population per district?
2. how to calculate time series per province?