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I am epidemiologist, not remote sensing expert. I am interested to find association between disease incidence /reported cases with urbanization (hypothesis " more bigger cities , more incidence".

Is there any dataset in GEE CATALOG from which to extract the extent of urbanization?

I did calculated urban index with Landsat and then estimated mean for each county but I am getting negative values. I do not why.

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  • Negative values in urban index means that the area with the negative values are Not Urban Areas and they are Rural Areas Jan 22 at 19:49
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you can use,

Normalized Difference Built-up Index (NDBI),

for this you can run following code in Google Earth Engine Code Editor

// point of interest 
var point = ee.Geometry.Point([80.62814, 7.29069]) 

// get land sat 8 images
var l8 = ee.ImageCollection('LANDSAT/LC08/C01/T1_TOA');

// Get the least cloudy image in 2020
var image = ee.Image(
  l8.filterDate('2013-01-01', '2020-12-31')
    .filterBounds(point)
    .sort('CLOUD_COVER')
    .first()
);

// NDBI = (SWIR – NIR) / (SWIR + NIR) 
//      = (Band 6 – Band 5) / (Band 6 + Band 5)


// NDBI Calculation
var swir = image.select('B6');
var nir = image.select('B5');
var ndbi = swir.subtract(nir).divide(swir.add(nir)).rename('NDBI');

// display 
Map.centerObject(point, 12);
var ndbiParams = {min: -1, max: 1, palette: ['white' , 'white', 'white', 'red' , 'red', 'red']};
Map.addLayer(ndbi, ndbiParams, 'NDBI');

change the point of interest var point = ee.Geometry.Point([???, ???]) for your preference. And there are more advance methods but this is the simplest method in the book

example -

Satellite Image enter image description here

analyzed outcome enter image description here

RED means estimated build-up area

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    I have used the code that was successful , for calculating means should I mask values equal to or greater than 0 ? Jan 23 at 9:24
  • Greater than 0 is the norm and all the values are in beween -1 and +1. But you have to fine tune the cut off point. Example like 0.15 for desert areas and 0.05 for areas in tropical climates and so on if you really needs an exact answer. Jan 23 at 11:55

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