Copy taxonomy term name to another field
I am assuming you have a content type with a field 
"Title" of type "Term Reference"... and you want to pass an address from this existing field to a hidden field for Geo coding or whatever else for that specific page. 

I would suggest using views and entity reference to do this. This method is useful for passing multiple fields, but can be used to grab just one...

Once you have the Entity Reference module enabled and installed create a view. For the view's display options (that + sign) add 'Entity Reference'.

Add a field to this view of type: "Content: All taxonomy terms"

In the next options screen you can limit the options here to your specific 'Cities' vocabulary.

You now need to add a contextual filter 'Content:NID' to get this view to only display the city term reference for the page that it's on.

Now go back to your content type and add a field of type 'Entity Reference'. Configure it like this:


Target Type - Node
Mode - Views (filter by an entity reference view)
View used to select the entities - 'my entity reference view'


Now add your Geofield and configure it to 'Geocode from another field' - i.e. your entity reference field (which you can hide in the display options)

In the event that a city name alone is insufficient to geocode from consider adding other fields to your content type and passing them to your entity reference view.