Google Earth Engine spatial join of nearest polygon to points

Question

I am trying to do a spatial join of two feature collections: points to watershed polygons. Many of the points are outside of the polygon area so I want to join the point to the nearest polygon. Ideally the output would be a table of points with the properties of the nearest watershed appended.

I have done a simple spatial join but my problems at the moment are:

1. This outputs all the nearest polygons in the search area; and
2. The output doesn't include the secondary feature collection properties in the output table.

How do I do this please?

Here is the code:

//var sg_fc: Table  //imported table of points

// Load the HydroATLAS dataset.
var basinATLAS = ee.FeatureCollection('WWF/HydroATLAS/v1/Basins/level12');

// Define a spatial filter, with distance 10 km.
var distFilter = ee.Filter.withinDistance({
  distance: 10000,
  leftField: '.geo',
  rightField: '.geo',
  maxError: 10
});

// Define a saveAll join.
var distSaveAll = ee.Join.saveAll({
  matchesKey: 'points',
  measureKey: 'distance',
  ordering: 'distance'
});

// Apply the join.
var spatialJoined = distSaveAll.apply(basinATLAS,sg_fc,distFilter);

Map.addLayer(spatialJoined, {}, 'spatial join');
Map.addLayer(sg_fc, {}, 'sites')

Export.table.toDrive(spatialJoined);

Link to code editor: https://code.earthengine.google.com/90243d26764b46441efc1b477db185cf

Answer 1

1. Don't use saveAll(), use saveBest().
2. You can't output nested features; only primitive objects (numbers, strings, geometries). You'll have to copy the parts of the saved feature you want (name, ID, whatever) into the primary feature.