Google Earth Engine Tutorial: Clip and Extract Population Data

Step 1: Load Population Data

Start by loading a global population dataset from the Google Earth Engine (GEE) catalog. A commonly used dataset is the Global Population Density Layer (GPD). Here’s an example code snippet:

var population = ee.Image('JRC/GHSL/P2016/POP_GPW4_GSAD30_V1');

Step 2: Define Region of Interest (ROI)

Create or load a geometry to define the area you want to clip. For example, using a built-in dataset like the WorldBorder:

var roi = ee.FeatureCollection('FAO/GAUL/WEEKLY').filter(ee.Filter.eq('ADM0_NAME', 'Kenya'));

Step 3: Clip the Population Data

Use the clip() method to restrict the population data to your ROI:

var clippedPopulation = population.clip(roi);

Step 4: Extract Summary Statistics

Calculate statistics such as mean, max, or total population within the clipped region:

var stats = clippedPopulation.reduceRegion({
  reducer: ee.Reducer.mean(),
  geometry: roi.geometry(),
  scale: 30,
  maxPixels: 1e9
});
print(stats.get('population'));

Step 5: Export Clipped Data

Export the clipped image as a GeoTIFF or CSV file for further analysis:

Export.image.toDrive({
  image: clippedPopulation,
  description: 'ClippedPopulation',
  fileNamePrefix: 'kenya_population',
  folder: 'GEE_Exports',
  scale: 30,
  crs: 'EPSG:4326',
  region: roi.geometry()
});

FAQ

• What population datasets are available in GEE? GEE provides datasets like JRC/GHSL/P2016/POP_GPW4_GSAD30_V1, USGS/GFSAD/2019, and others. Check the GEE Data Catalog for details.
• How do I handle large regions? Use the region parameter in reduceRegion or split the region into smaller tiles for processing.
• Why is the clipped area showing null values? Ensure the ROI geometry is valid and properly defined. Check for projection mismatches using crs or projection parameters.
• Can I export data to CSV instead of GeoTIFF? Yes, use Export.table.toDrive() with reduceRegion results to export as CSV.
• What if I encounter access errors? Verify your GEE account has the necessary permissions and that the dataset is publicly accessible.