What scale to specify when getting a summary statistic for an entire country?

Question

I am trying to calculate the population in a country as follows:

//Population per square km:
var pop_count = ee.ImageCollection("CIESIN/GPWv411/GPW_Population_Count").filter(ee.Filter.date('2020-01-01', '2020-12-31')).mean();
//Country specified:
var country = ee.FeatureCollection("FAO/GAUL_SIMPLIFIED_500m/2015/level0").filter(ee.Filter.eq('ADM0_NAME', 'South Africa'))

//Population in entire country
var pop_country = pop_count.reduceRegion({
  reducer: ee.Reducer.sum(),
  geometry: country.geometry(),
  //scale: ???
})

I get an error if I don't specify scale, but I want one number (population) for the entire country. What scale should I specify?

Answer 1

You can take the native scale of the data you are using:

var scale = ee.ImageCollection("CIESIN/GPWv411/GPW_Population_Count")
                .first().projection().nominalScale())
print(scale)

Or look at the data catalog entry of the data and take the scale from there. (Unfortunately for GPWv411 the scale is 30 arc seconds which you then would have to convert to meters. So the first solution requires a bit less effort).