ee.FeatureCollection.map

  • map() iterates over a FeatureCollection, applying a user-defined function to each feature.

  • The provided function transforms features and returns modified versions, creating a new FeatureCollection.

  • map() allows adding/modifying properties of features within a FeatureCollection or performing calculations based on existing properties.

  • An optional dropNulls parameter controls whether features resulting in null from the mapping function are retained in the output.

Maps an algorithm over a collection.

Returns the mapped collection.

UsageReturns
FeatureCollection.map(algorithm, dropNulls)Collection
ArgumentTypeDetails
this: collectionCollectionThe Collection instance.
algorithmFunctionThe operation to map over the images or features of the collection. A JavaScript function that receives an image or features and returns one. The function is called only once and the result is captured as a description, so it cannot perform imperative operations or rely on external state.
dropNullsBoolean, optionalIf true, the mapped algorithm is allowed to return nulls, and the elements for which it returns nulls will be dropped.

Examples

Code Editor (JavaScript)

// FeatureCollection of power plants in Belgium.
var fc = ee.FeatureCollection('WRI/GPPD/power_plants')
            .filter('country_lg == "Belgium"');

// Function to convert power plant capacity from megawatts to gigawatts and
// add the value as a new feature property.
var mwToGw = function(feature) {
  var megawatt = feature.getNumber('capacitymw');
  var gigawatt = megawatt.divide(1000);
  return feature.set('capacitygw', gigawatt);
};

// Apply the function to each feature in the collection.
fc = fc.map(mwToGw);

print('Note the new "capacitygw" property in each feature', fc);

Python setup

See the Python Environment page for information on the Python API and using geemap for interactive development.

import ee
import geemap.core as geemap

Colab (Python)

# FeatureCollection of power plants in Belgium.
fc = ee.FeatureCollection('WRI/GPPD/power_plants').filter(
    'country_lg == "Belgium"')

# Function to convert power plant capacity from megawatts to gigawatts and
# add the value as a new feature property.
def mw_to_gw(feature):
  megawatt = feature.getNumber('capacitymw')
  gigawatt = megawatt.divide(1000)
  return feature.set('capacitygw', gigawatt)

# Apply the function to each feature in the collection.
fc = fc.map(mw_to_gw)

print('Note the new "capacitygw" property in each feature:', fc.getInfo())