The instructions for this is confusing because both the city and the township field helps say to enter municipalities in those fields. But Gainsborough is only a township. I'll tell you what I do when I review these and you can ignore me or not. When I know a municipality is not a city but is only a township, and the indexer enters it only in the township field, I let it go. When he enters it in both fields I let it go because of the written instructions, even though it's not a city. Occasionally "Township" will be written with the name on the municipality line, in which case I would only accept the name entered into the township field.
The field help for city states:
Index municipalities, cities, or towns recorded in the header of the document in this field. Do not index any places recorded in the "Residence" or "Address" columns.
The header of the image you are working on shows: Municipality Gainsborough .
so according to the field help, it should be under city.
Hope that helps.