GEE Code

var district = ee.FeatureCollection("projects/gee-cindy-250304/assets/ws");

var dsize = district.size();
print(dsize);

var district_geometry = district.geometry();

Map.centerObject(district_geometry,12);
Map.addLayer(district);

function maskS2clouds(image) {
  var qa = image.select('QA60');

  // Bits 10 and 11 are clouds and cirrus, respectively.
  var cloudBitMask = 1 << 10;
  var cirrusBitMask = 1 << 11;

  // Both flags should be set to zero, indicating clear conditions.
  var mask = qa.bitwiseAnd(cloudBitMask).eq(0)
      .and(qa.bitwiseAnd(cirrusBitMask).eq(0));

  return image.updateMask(mask).divide(10000);
}


// Map the function over one year of data.
// Load Sentinel-2 TOA reflectance data.
var dataset = ee.ImageCollection("COPERNICUS/S2_HARMONIZED")
                  .filterBounds(district_geometry)
                  .filterDate('2019-01-01', '2020-01-01')
                  // Pre-filter to get less cloudy granules.
                  .filter(ee.Filter.lt('CLOUDY_PIXEL_PERCENTAGE', 10))
                  .map(maskS2clouds);

var rgbVis = {
  min: 0.0,
  max: 0.3,
  bands: ['B4', 'B3', 'B2'],
};


Map.addLayer(dataset.median(), rgbVis, 'RGB');

//export data
var exportdataset =  ee.ImageCollection('COPERNICUS/S2_HARMONIZED')
                  .filterBounds(district_geometry)
                  .filterDate('2019-01-01', '2020-01-01')
                  // Pre-filter to get less cloudy granules.
                  .filter(ee.Filter.lt('CLOUDY_PIXEL_PERCENTAGE', 10))
                  .map(maskS2clouds)
                  .select(['B4', 'B3', 'B2']);

  var mosaic = exportdataset.mosaic();

  Export.image.toDrive({
      image: mosaic,
      description:'Yunshan-Yunnan',
      scale: 10,
      maxPixels: 1e13,
      region:district_geometry,
      fileFormat: 'GeoTIFF',
      formatOptions: {
        cloudOptimized: true
      }
    });