I have a similar need to plot based on a zipcode that is already in splunk. I'm not much of a Splunk Guru but I was able to make it work using an automatic lookup.
Query: A4 OR A5 OR A6 OR A8 | geonormalize
Lookup input fields
ZipCode = ZipCode
Lookup output fields
lat = lat
lng = lng
Lookup table
ZipCode,lat,lng
80809,38.921314,-104.993684
60047,42.1969444,-88.0933333
T2E 0B2,51.1,-114.1
My Data
Model=A6 Price=27000 ZipCode=80809
Model=A6 Price=27000 ZipCode=60047
Model=A8 Price=19000 ZipCode=80809
Model=A8 Price=19000 ZipCode=60047
Model=A8 Price=35000 ZipCode=80809
Model=A8 Price=35000 ZipCode=60047
Model=A5 Price=35000 ZipCode=60047
Model=A4 Price=28808 ZipCode=’T2E 0B2’
... View more