In Progess: Getting Started With Google's Earth Engine

May 24, 2022

In this blog post, I show two usecases of the Google Earth Engine for Economic research.

What is the Google Earth Engine?

Google’s Earth Engine is a powerful tool to process large amounts of satellite data.
Common uses include calculating nightlights, elevation, or population statistics.

Some advantages of the Earth Engine:

Large number of satellite products directly available on Google's Servers

All calculations are run in the cloud

You can check out a number of highlighted case studies directly at Case Studies. To use the Earth Engine by yourself, you are required to register (for free).

Earth Engine for Economics

Case Study 1: Measuring Urban Sprawl from Space

This case study is based on the excellent tutorial for raster to vector conversion. The tutorial shows how to delimit areas by their night light intensity. To measure urban sprawl, I extend the code by a time dimension.

Step 1: Replicate Tutorial

// Load a Japan boundary from the Large Scale International Boundary dataset.
var japan = ee.FeatureCollection('USDOS/LSIB_SIMPLE/2017')
  .filter(ee.Filter.eq('country_na', 'Japan'));

// Load a 2012 nightlights image, clipped to the Japan border.
var nl2012 = ee.Image('NOAA/DMSP-OLS/NIGHTTIME_LIGHTS/F182012')
  .select('stable_lights')
  .clipToCollection(japan);

// Define arbitrary thresholds on the 6-bit nightlights image.
var zones = nl2012.gt(30).add(nl2012.gt(55)).add(nl2012.gt(62));
zones = zones.updateMask(zones.neq(0));

// Convert the zones of the thresholded nightlights to vectors.
var vectors = zones.addBands(nl2012).reduceToVectors({
  geometry: japan,
  crs: nl2012.projection(),
  scale: 1000,
  geometryType: 'polygon',
  eightConnected: false,
  labelProperty: 'zone',
  reducer: ee.Reducer.mean()
});

// Display the thresholds.
Map.setCenter(139.6225, 35.712, 9);
Map.addLayer(zones, {min: 1, max: 3, palette: ['0000FF', '00FF00', 'FF0000']}, 'raster');

// Make a display image for the vectors, add it to the map.
var display = ee.Image(0).updateMask(0).paint(vectors, '000000', 3);
Map.addLayer(display, {palette: '000000'}, 'vectors');