Creation custom dependent fields

Hello, I have taxonomy term "City", that have geofiled with coordinates.
On the entity "Organization" I have reference to City and another geofield - coordinates.

How to make propagation of City.coordinates to organization.coordinates during form filling after user selects reference to city taxonomy in field organization.city?

I know how to configure propagation after Node-organization saving. It work fine. But I want help User to find approximate coordinates right on creation.