ReduceRegion(s) Google Earth Engine Python API

Question

I'm trying to find the area of a classified land cover across the study area using the Google Earth Engine's Python API. I am trying to do this by mapping a .reduceRegion function across the image collection using the approach below.

# Salt marsh extents are images where pixels = 1 if salt marsh has been detected

salt_marsh_area = salt_marsh_extents.map(lambda image:
                                      image.reduceRegion(
                                          reducer=ee.Reducer.sum(),
                                          geometry=whole_estuary.geometry(),
                                          scale=30
                                      ))

However, when I try and export this to my Google Drive or use a .getInfo() to inspect the result I get an error of ee.ee_exception.EEException: Collection.map: A mapped algorithm must return a Feature or Image.

How do you convert this into a table format for export?

Answer 1

.reduceRegion() returns an ee.Dict. You can use this, wrap it into an ee.Feature without setting a geometry and return that feature. In the end you can export this Feature Collection as a CSV to get a table with your values. This is how you would do it:

def reduce_salt(image):
  reduced = image.reduceRegion(
              reducer=ee.Reducer.sum(),
              geometry=whole_estuary.geometry(),
              scale=30)
  return ee.Featue(None, reduced)

salt_marsh_area = salt_marsh_extents.map(reduce_salt)

task = ee.batch.Export.table.toDrive(
  collection=salt_marsh_area,
  description='reduced',
  fileFormat='CSV'
);

task.start()