With exception of Cornwall and Lancaster, other Dukedoms are designated as symbolic and are not linked to the geographical designations, except by tradition. In olden days, pre Stuart times, a Dukedom generally did come in the form of a Duchy so to speak, but this altered over time.
I do not believe that the present Duke of York has any entailed property in Yorkshire or York, nor the Dukes of Edinburgh, Gloucester and Kent in their titular cities or counties either! Their income is likewise unrelated to their geographical designations. I believe that their Dukedoms being long regarded as the preserve of the RF are recreated out of symbolic tradition. I often ponder if William and Harry will become Dukes upon marriage during their grandmother's lifetime. If so, I tend to think that as Cumberland and Teviotdale and Albany remain 'sensitive', that perhaps Clarence, Cambridge, Kendal or Sussex could be revived.
On a non Royal basis, a similar situation occurs in the Dukedoms of the realm. Originally the Dukes of Norfolk held vast tracts in Norfolk but after inheriting estates in Nottinghamshire, Sussex and Sheffield gradually divested themselves of their Norfolk holdings and made their home in Nottinghamshire before making Arundel in Sussex the main ducal seat. The Dukes of Bedford are one of the few ducal dynasties that still reside in their titular county. The Devonshire Dukedom has never had any significant links with that county! The Dukes of Northumberland like the Dukes of Bedford are seated in their titular county! In Scotland most Dukedoms do tend to still be linked to geographical areas!
It is actually quite fascinating that the present Duke of Somerset, who owns very few acres in that county but quite a lot in Wiltshire and Devonshire, is the only one who officially refers to his holdings as a Duchy. I assume that this is because the dukedom was created in exceptional circumstances when the Earl of Hertford as Lord Protector made himself Duke with the agreement of parliament as opposed to normal letters patent!