By Latitude / Longitude disabled

I have a number of small towns in my model that are unable to be resolved by name. I would like to use latitude and longitude to resolve these towns. Following the Lumira 1.15 User guide, I created latitude and longitude measures with a numeric types. I then go to "Create a geographic hierarchy..." > "By Latitude / Longitude" but the field is greyed out and unselectable. My data source is HANA. Any ideas on what I'm doing wrong?