Any one of the above options may be used. Determine which is applicable to your organization. The determining factor relates to the uniqueness of the ID. For instance, if the location name of your records is not unique per location then you must submit either a combination of location name and location number, or location number (assuming each record contains a unique location number).
Input the applicable column header or headers to your location file when you intend to update existing records. Keep in mind, that If only one identifying column is specified, then that value must be unique for that field among all of the locations in your organization or a lookup error will occur. The name and number fields together are already guaranteed by the system to be unique among your organization’s locations.
If the rows included in the file will result in all new records then it is not necessary to include the identifying column. Create separate files for location updates versus location additions.