How do i assign value to geo type field

Users Dgraph
,
5

From the example if i define geo predicate like below
loc: geo @index(geo) .

do i still need to set ^^geo:geojson . during mutation below ? why its already known

 <_:0xeb1dde9c> <loc> "{'type':'Point','coordinates':[-122.4220186,37.772318]}"^^<geo:geojson> .