Migrating to Drupal 8 geofields

The "geofield_latlon" migration process plugin supports the migration of latitude/longitude values to drupal 8 field type "geofield" values.
As of this writing, this patch is needed.
You can see the issue here.

The source value passed to the geofield_latlon plugin needs to be an array whose first value is a latitude and second value is a longitude. For example, to populate a geofield named 'field_drupal8_geofield' when your source row contains "latitude" and "longitude" properties:

process:
  field_drupal8_geofield:
    plugin: geofield_latlon
    source:
      - latitude
      - longitude

When migrating from a Drupal 7 site, the source property for a geofield is already in the proper format, so (if your field name is field_drupal7_geofield), simply do:

process:
  field_drupal8_geofield:
    plugin: geofield_latlon
    source: field_drupal7_geofield