How can I use the latitude and longitude form fields to position the map markers?
The Maps Premium View (or the Map widget and the Entry Map field) requires to setup an address form field as the source to geocode the map markers. That Address field is by default a standard Gravity Forms address field type. You may use a different field type as the address source.
If you have the position coordinates (latitude and longitude) stored as form fields, you may also use them instead of the Address to position the markers over the map.
When using the Maps Premium View extension, in order to override the Address Field setting replacing it by the coordinates fields, you may use the filter hook
gravityview/maps/markers/lat_long/fields_id as in the following example: