如需对 FeatureCollection
中的每个 Feature
应用相同的操作,请使用 featureCollection.map()
。例如,如需向流域 FeatureCollection
中的每个地图项添加另一个面积属性,请使用以下命令:
Code Editor (JavaScript)
// Load watersheds from a data table. var sheds = ee.FeatureCollection('USGS/WBD/2017/HUC06'); // This function computes the feature's geometry area and adds it as a property. var addArea = function(feature) { return feature.set({areaHa: feature.geometry().area().divide(100 * 100)}); }; // Map the area getting function over the FeatureCollection. var areaAdded = sheds.map(addArea); // Print the first feature from the collection with the added property. print('First feature:', areaAdded.first());
import ee import geemap.core as geemap
Colab (Python)
# Load watersheds from a data table. sheds = ee.FeatureCollection('USGS/WBD/2017/HUC06') # Map an area calculation function over the FeatureCollection. area_added = sheds.map( lambda feature: feature.set( {'areaHa': feature.geometry().area().divide(100 * 100)} ) ) # Print the first feature from the collection with the added property. display('First feature:', area_added.first())
在前面的示例中,请注意,系统会根据地图项的几何图形进行计算,然后设置新属性。您还可以使用涉及现有属性的计算来设置属性。
可以使用 map()
生成全新的 FeatureCollection
。
以下示例将流域转换为质心:
Code Editor (JavaScript)
// This function creates a new feature from the centroid of the geometry. var getCentroid = function(feature) { // Keep this list of properties. var keepProperties = ['name', 'huc6', 'tnmid', 'areasqkm']; // Get the centroid of the feature's geometry. var centroid = feature.geometry().centroid(); // Return a new Feature, copying properties from the old Feature. return ee.Feature(centroid).copyProperties(feature, keepProperties); }; // Map the centroid getting function over the features. var centroids = sheds.map(getCentroid); // Display the results. Map.addLayer(centroids, {color: 'FF0000'}, 'centroids');
import ee import geemap.core as geemap
Colab (Python)
# This function creates a new feature from the centroid of the geometry. def get_centroid(feature): # Keep this list of properties. keep_properties = ['name', 'huc6', 'tnmid', 'areasqkm'] # Get the centroid of the feature's geometry. centroid = feature.geometry().centroid() # Return a new Feature, copying properties from the old Feature. return ee.Feature(centroid).copyProperties(feature, keep_properties) # Map the centroid getting function over the features. centroids = sheds.map(get_centroid) # Display the results. m = geemap.Map() m.set_center(-96.25, 40, 4) m.add_layer(centroids, {'color': 'FF0000'}, 'centroids') m
请注意,只有部分属性会传播到新集合中的地图项。