本文仅仅是将GEE官网上的代码整理一下，一方面自学，另一方面自我监督。文中有些问题是我想不通的，还需经历时间来理解。
3 feature collection
3.1 from polygons
官网上给的代码截图：
逐行分析代码：
// Create and render a feature collection from polygons.##从多边形，创建和反馈特征集
// Construct a FeatureCollection from a list of features.##构建属性集
var fc = ee.FeatureCollection([
// Create each feature with a geometry and properties.##创建每一个图形的几何特征和属性值
ee.Feature(
ee.Geometry.Polygon({
coords: [[-109.05, 41], [-109.05, 37], [-102.05, 37], [-102.05, 41]],
geodesic: false, // The state boundaries are not geodesic.##边界不是测地线。测地线是曲面上面两点最短的距离。
maxError: 1000 // Make the error margin large; we don't need accuracy.
}), {name: 'Colorado', fill: 1}), // Pass properties as a dictionary.
ee.Feature(
ee.Geometry.Polygon({
coords: [
[-114.05, 37.0], [-109.05, 37.0], [-109.05, 41.0],
[-111.05, 41.0], [-111.05, 42.0], [-114.05, 42.0]
],
geodesic: false,
maxError: 1000
}), {name: 'Utah', fill: 2})
]);
// Fill, then outline the polygons into a blank image.##填充，然后把外边框放到一个image中。
var image = ee.Image()
.paint(fc, 'fill') // Get color from property named 'fill'
.paint(fc, 3, 5) // Outline using color 3, width 5.##外边框的颜色和宽度。颜色3是蓝色，1是红，2是绿。
.toByte();
Map.addLayer(image, {
palette: ['000000', 'FF0000', '00FF00', '0000FF'],
max: 3,##调节颜色。
opacity: 0.5
});
Map.setCenter(-107, 41, 6);
3.2 buffer
官网上给的代码截图：
逐行分析代码：
// Feature buffer example.
// Display the area within 2 kilometers of San Francisco BART stations.
// Instantiate a FeatureCollection of BART locations in Downtown San Francisco ##用例子说明地铁站的特征集
// (points).##找到三个点。
var stations = [
ee.Feature(
ee.Geometry.Point(-122.42, 37.77), {'name': '16th St. Mission (16TH)'}),
ee.Feature(
ee.Geometry.Point(-122.42, 37.75), {'name': '24th St. Mission (24TH)'}),
ee.Feature(
ee.Geometry.Point(-122.41, 37.78),
{'name': 'Civic Center/UN Plaza (CIVC)'})
];
var bartStations = ee.FeatureCollection(stations);
// Map a function over the collection to buffer each feature.##构建一个函数，让
var buffered = bartStations.map(function(f) {##map里面有多个function，butter是其中的一个。
return f.buffer(2000, 100); // Note that the errorMargin is set to 100.
});
Map.addLayer(buffered, {color: '800080'});
Map.setCenter(-122.4, 37.7, 11);
3.3 computed area filter
官网上给的代码截图：
逐行分析代码：
// Computed area filter.
// Find US counties smaller than 3k square kilometers in area.##选择县域面积小于3000平方千米的县城。
// Load counties from TIGER boundaries table
var counties = ee.FeatureCollection('TIGER/2016/Counties');
// Map a function over the counties to set the area of each.##设置一个函数，获得每一个面积值。
var countiesWithArea = counties.map(function(f) {##点后面是函数
// Compute area in square meters. Convert to hectares.##平方米转到公顷。
var areaHa = f.area().divide(100 * 100);
// A new property called 'area' will be set on each feature.
return f.set({area: areaHa});
});
// Filter to get only smaller counties.
var smallCounties = countiesWithArea.filter(ee.Filter.lt('area', 3e5));##现在单位是公顷，面积小于300 000公顷。也就是面积小于300 000 0000平方米。3000 000 000平方米就是3千平方千米。
Map.addLayer(smallCounties, {color: '900000'});##颜色是红色
Map.setCenter(-119.7, 38.26, 7);
3.4 distance
官网上给的代码截图：
逐行分析代码：
// Collection.distance example.
// Computes the distance to the nearest feature in a collection.
// Construct a FeatureCollection from a list of geometries.
var fc = ee.FeatureCollection([##设置三个点
ee.Geometry.Point(-72.94411, 41.32902),
ee.Geometry.Point(-72.94411, 41.33402),
ee.Geometry.Point(-72.94411, 41.33902),
// The geometries do not need to be the same type.
ee.Geometry.LineString(##设置一条线段，线段有三个点。
-72.93411, 41.30902, -72.93411, 41.31902, -72.94411, 41.31902)
]);
// Compute distance from the dfeatures, to a max of 1000 meters.
var distance = fc.distance(1000, 100);##1000是缓冲距离，100不知道什么意思。
Map.setCenter(-72.94, 41.32, 13);
Map.addLayer(distance, {min: 0, max: 1000, palette: ['yellow', 'red']});
Map.addLayer(fc);
3.5 join
官网上给的代码截图：
逐行分析代码：
// Simple Join example.
// Show parks in San Francisco within 2 kilometers of a BART station.##显示在地铁站2千米范围内的公园。
// Load fusion tables for BART station locations and local parks.
var bart = ee.FeatureCollection('GOOGLE/EE/DEMOS/bart-locations');
var parks = ee.FeatureCollection('GOOGLE/EE/DEMOS/sf-parks');
// Create a filter to pass the left features within 2km of the right features.##创建一个滤波通过左的数据（在右边数据的2km内）
var joinFilter = ee.Filter.withinDistance({
distance: 2000,
leftField: '.geo',
rightField: '.geo'
});
// Apply the join. The leftField corresponds to the primary collection##应用join功能，左边数据是主要的，右边数据是次要的。匹配条件是设定的过滤器。
// and the rightField corresponds to the secondary collection. The
// matching condition is specified by the filter.
var closeParks = ee.Join.simple().apply({
primary: parks,
secondary: bart,
condition: joinFilter
});
// Buffer the bart stations by 2km for display purposes.
var bufferedBart = bart.map(function(f) { return f.buffer(2000, 100); });
Map.setCenter(-122.45, 37.75, 13);
Map.addLayer(bufferedBart, {color: 'b0b0b0'});
Map.addLayer(closeParks, {color: '008000'});
3.6 reduce to image
官网上给的代码截图：
逐行分析代码：
// Example of FeatureCollection.reduceToImage()
// Define a feature collection with a value we want to average.
var fc = new ee.FeatureCollection([
ee.Feature(
ee.Geometry.Rectangle(
-122.4550, 37.8035,
-122.4781, 37.7935),
{'value': 0}),
ee.Feature(
ee.Geometry.Polygon([
[-122.4427, 37.8027],
[-122.4587, 37.7987],
[-122.4440, 37.7934]]),
{'value': 1})
]);
// Reduce the collection to an image, where each pixel##每一个像元是所有的feature（相交在某像元上）的中间值。
// is the mean of the 'value' property in all features
// intersecting that pixel.
var image_reduced = fc.reduceToImage(['value'], 'mean');
Map.setCenter(-122.4561, 37.7983, 14);
Map.addLayer(image_reduced, {
min: 0,
max: 1,
palette: ['008800', '00FF00']});
问题：不知道这个有什么用场。
3.7 from eargh engine asset
官网上给的代码截图：
逐行分析代码：
// Create a FeatureCollection from an Earth Engine Table.##创建一个特征集。
// Load census roads.##提取道路，先把州际的挑出来，再把地表的挑出来。
var roads = ee.FeatureCollection('TIGER/2016/Roads');
// Get only interstates.
var interstates = roads.filter(ee.Filter.eq('rttyp', 'I'));
// Get only surface roads.
var surfaceRoads = roads.filter(ee.Filter.eq('rttyp', 'M'));
// Display the roads in different colors.
Map.addLayer(surfaceRoads, {color: 'gray'}, 'surface roads');
Map.addLayer(interstates, {color: 'red'}, 'interstates');
这次的学习就到这里了，希望帮助自己学到知识， 也可以帮助到需要的朋友。不足之处，还望见谅。
我是小白，生产不了代码。copyright from Google earth engine。