Getting population by country using Google Earth Engine

Question

I was trying to get the population by country by using GEE. I tried the following code:

// world population 2015
var pop = ee.Image("JRC/GHSL/P2016/POP_GPW_GLOBE_V1/2015");
print(pop);
Map.addLayer(pop,{},'Population');

//world boundaries
var bound = ee.FeatureCollection("USDOS/LSIB_SIMPLE/2017");
print(bound);
Map.addLayer(bound,{},'boundaries');

// Getting Pop-2015 By country
var popcountry = pop.reduceRegions({
  collection:bound,
  reducer: ee.Reducer.sum(),
  scale: 250,
  });
print(popcountry);
Map.addLayer(popcountry,{},'PopC');

The issues that I see are the followings:

1. I only get a global population about 1 billions instead of about 7 bn.;

2. Many countries are zeros;

3. I tried to use different boundaries (specifically GADM), but I can't get any results as it appears something like an internal error has ocurred.

Answer 1

I 'think' you should specifically set a crs in the reduceRegions function. As the calculation will run out of time (reprojection in different projection takes a lot of time), you should export the result to get a proper result.

// Getting Pop-2015 By country
var popcountry = pop.reduceRegions({
  collection:bound,
  reducer: ee.Reducer.sum(),
  scale: 250,
  crs: 'EPSG:4326', // world wide crs which seems to work for me
  });

Export.table.toAsset(popcountry.limit(10), 'worldPopTest', 'worldPopTest')

Note that I tried first setting the original crs (and crsTransform) as projection, but that did not work (I think due to this: link forum, link projections). Therefore I choose the crs EPSG:4326 and results seems to match the real populations.

link code