I am reducing an image collection into a feature collection by using a function to map the reduceRegions function to each image in a collection. I'm trying to make sure the system:time_start property is carried over. My code is below

var DHW_region = DHW.map(function(image){
  return image
  collection:reefsEdit , 
  scale: 30

 DHW_region = DHW_region.flatten();

However, it doesn't seem to work and I'm getting an error

FeatureCollection (Error)
Error in map(ID=0): Dictionary: Unrecognized arguments to Dictionary constructor.

Where am I going wrong with this? Link to my code is here

  • you should share the collections (DHW_region and reefsEdit) or make proxy ones so we can reproduce the error Commented Jan 28, 2021 at 11:00
  • Thanks I have added a link to my code. Line 164. Run the code and you should see the error. thanks. Commented Jan 28, 2021 at 12:23

1 Answer 1


The argument of .set() should be as follows (see docs):

var_args (VarArgs): Either a dictionary of properties, or a vararg sequence of properties, e.g. key1, value1, key2, value2, ..

In your code, you set an ee.Date() as argument for .set(). You should 1) make a a vararg sequence of properties or 2) make a dictionary of properties:


.set({'system:time_start',: image.date()})

link code

  • ah OK thanks, that stops the error Commented Jan 29, 2021 at 10:07

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